Difference between revisions of "2001 AMC 12 Problems"

Latest revision as of 11:53, 24 January 2024

2001 AMC 12 (Answer Key) Printable versions: Wiki • AoPS Resources • PDF
Instructions This is a 25-question, multiple choice test. Each question is followed by answers marked A, B, C, D and E. Only one of these is correct. You will receive 6 points for each correct answer, 2.5 points for each problem left unanswered if the year is before 2006, 1.5 points for each problem left unanswered if the year is after 2006, and 0 points for each incorrect answer. No aids are permitted other than scratch paper, graph paper, ruler, compass, protractor and erasers (and calculators that are accepted for use on the test if before 2006. No problems on the test will require the use of a calculator). Figures are not necessarily drawn to scale. You will have 75 minutes working time to complete the test.
1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25

Problem 1

The sum of two numbers is $S$ . Suppose $3$ is added to each number and then each of the resulting numbers is doubled. What is the sum of the final two numbers?

$\text{(A)}\ 2S + 3\qquad \text{(B)}\ 3S + 2\qquad \text{(C)}\ 3S + 6 \qquad\text{(D)} 2S + 6 \qquad \text{(E)}\ 2S + 12$

Solution

Problem 2

Let $P(n)$ and $S(n)$ denote the product and the sum, respectively, of the digits of the integer $n$ . For example, $P(23) = 6$ and $S(23) = 5$ . Suppose $N$ is a two-digit number such that $N = P(N)+S(N)$ . What is the units digit of $N$ ?

$\text{(A)}\ 2\qquad \text{(B)}\ 3\qquad \text{(C)}\ 6\qquad \text{(D)}\ 8\qquad \text{(E)}\ 9$

Solution

Problem 3

The state income tax where Kristin lives is levied at the rate of $p\%$ of the first $\textdollar 28000$ of annual income plus $(p + 2)\%$ of any amount above $\textdollar 28000$ . Kristin noticed that the state income tax she paid amounted to $(p + 0.25)\%$ of her annual income. What was her annual income?

$\text{(A)}\ $28000\qquad \text{(B)}\ $32000\qquad \text{(C)}\ $35000\qquad \text{(D)}\ $42000\qquad \text{(E)}\ $56000$

Solution

Problem 4

The mean of three numbers is $10$ more than the least of the numbers and $15$ less than the greatest. The median of the three numbers is $5$ . What is their sum?

$\text{(A)}\ 5\qquad \text{(B)}\ 20\qquad \text{(C)}\ 25\qquad \text{(D)}\ 30\qquad \text{(E)}\ 36$

Solution

Problem 5

What is the product of all positive odd integers less than 10000?

$\text{(A)}\ \dfrac{10000!}{(5000!)^2}\qquad \text{(B)}\ \dfrac{10000!}{2^{5000}}\qquad \text{(C)}\ \dfrac{9999!}{2^{5000}}\qquad \text{(D)}\ \dfrac{10000!}{2^{5000} \cdot 5000!}\qquad \text{(E)}\ \dfrac{5000!}{2^{5000}}$

Solution

Problem 6

A telephone number has the form $\text{ABC-DEF-GHIJ}$ , where each letter represents a different digit. The digits in each part of the number are in decreasing order; that is, $A > B > C$ , $D > E > F$ , and $G > H > I > J$ . Furthermore, $D$ , $E$ , and $F$ are consecutive even digits; $G$ , $H$ , $I$ , and $J$ are consecutive odd digits; and $A + B + C = 9$ . Find $A$ .

$\text{(A)}\ 4\qquad \text{(B)}\ 5\qquad \text{(C)}\ 6\qquad \text{(D)}\ 7\qquad \text{(E)}\ 8$

Solution

Problem 7

A charity sells $140$ benefit tickets for a total of $\textdollar 2001$ . Some tickets sell for full price (a whole dollar amount), and the rest sells for half price. How much money is raised by the full-price tickets?

$\text{(A) }$782\qquad \text{(B) }$986\qquad \text{(C) }$1158\qquad \text{(D) }$1219\qquad \text{(E) }$1449$

Solution

Problem 8

Which of the cones listed below can be formed from a $252^\circ$ sector of a circle of radius $10$ by aligning the two straight sides?

$[asy] import graph; unitsize(1.5cm); defaultpen(fontsize(8pt)); draw(Arc((0,0),1,-72,180),linewidth(.8pt)); draw(dir(288)--(0,0)--(-1,0),linewidth(.8pt)); label("$10$",(-0.5,0),S); draw(Arc((0,0),0.1,-72,180)); label("$252^{\circ}$",(0.05,0.05),NE); [/asy]$

$\text{(A) A cone with slant height of } 10 \text{ and radius } 6$

$\text{(B) A cone with height of } 10 \text{ and radius } 6$

$\text{(C) A cone with slant height of } 10 \text{ and radius } 7$

$\text{(D) A cone with height of } 10 \text{ and radius } 7$

$\text{(E) A cone with slant height of } 10 \text{ and radius } 8$

Solution

Problem 9

Let $f$ be a function satisfying $f(xy) = \frac{f(x)}y$ for all positive real numbers $x$ and $y$ . If $f(500) =3$ , what is the value of $f(600)$ ?

$\text{(A)}\ 1 \qquad \text{(B)}\ 2 \qquad \text{(C)}\ \frac52 \qquad \text{(D)}\ 3 \qquad \text{(E)}\ \frac{18}5$

Solution

Problem 10

The plane is tiled by congruent squares and congruent pentagons as indicated. The percent of the plane that is enclosed by the pentagons is closest to

$\text{(A) }50 \qquad \text{(B) }52 \qquad \text{(C) }54 \qquad \text{(D) }56 \qquad \text{(E) }58$

$[asy] unitsize(3mm); defaultpen(linewidth(0.8pt)); path p1=(0,0)--(3,0)--(3,3)--(0,3)--(0,0); path p2=(0,1)--(1,1)--(1,0); path p3=(2,0)--(2,1)--(3,1); path p4=(3,2)--(2,2)--(2,3); path p5=(1,3)--(1,2)--(0,2); path p6=(1,1)--(2,2); path p7=(2,1)--(1,2); path[] p=p1^^p2^^p3^^p4^^p5^^p6^^p7; for(int i=0; i<3; ++i) { for(int j=0; j<3; ++j) { draw(shift(3*i,3*j)*p); } } [/asy]$

Solution

Problem 11

A box contains exactly five chips, three red and two white. Chips are randomly removed one at a time without replacement until all the red chips are drawn or all the white chips are drawn. What is the probability that the last chip drawn is white?

$\text{(A) }\frac {3}{10} \qquad \text{(B) }\frac {2}{5} \qquad \text{(C) }\frac {1}{2} \qquad \text{(D) }\frac {3}{5} \qquad \text{(E) }\frac {7}{10}$

Solution

Problem 12

How many positive integers not exceeding $2001$ are multiples of $3$ or $4$ but not $5$ ?

$\text{(A) }768 \qquad \text{(B) }801 \qquad \text{(C) }934 \qquad \text{(D) }1067 \qquad \text{(E) }1167$

Solution

Problem 13

The parabola with equation $y=ax^2+bx+c$ and vertex $(h,k)$ is reflected about the line $y=k$ . This results in the parabola with equation $y=dx^2+ex+f$ . Which of the following equals $a+b+c+d+e+f$ ?

$\text{(A) }2b \qquad \text{(B) }2c \qquad \text{(C) }2a+2b \qquad \text{(D) }2h \qquad \text{(E) }2k$

Solution

Problem 14

Given the nine-sided regular polygon $A_1 A_2 A_3 A_4 A_5 A_6 A_7 A_8 A_9$ , how many distinct equilateral triangles in the plane of the polygon have at least two vertices in the set $\{A_1,A_2,\dots,A_9\}$ ?

$\text{(A) }30 \qquad \text{(B) }36 \qquad \text{(C) }63 \qquad \text{(D) }66 \qquad \text{(E) }72$

Solution

Problem 15

An insect lives on the surface of a regular tetrahedron with edges of length 1. It wishes to travel on the surface of the tetrahedron from the midpoint of one edge to the midpoint of the opposite edge. What is the length of the shortest such trip? (Note: Two edges of a tetrahedron are opposite if they have no common endpoint.)

$\text{(A) }\frac {1}{2} \sqrt {3} \qquad \text{(B) }1 \qquad \text{(C) }\sqrt {2} \qquad \text{(D) }\frac {3}{2} \qquad \text{(E) }2$

Solution

Problem 16

A spider has one sock and one shoe for each of its eight legs. In how many different orders can the spider put on its socks and shoes, assuming that, on each leg, the sock must be put on before the shoe?

$\text{(A) }8! \qquad \text{(B) }2^8 \cdot 8! \qquad \text{(C) }(8!)^2 \qquad \text{(D) }\frac {16!}{2^8} \qquad \text{(E) }16!$

Solution

Problem 17

A point $P$ is selected at random from the interior of the pentagon with vertices $A = (0,2)$ , $B = (4,0)$ , $C = (2 \pi + 1, 0)$ , $D = (2 \pi + 1,4)$ , and $E=(0,4)$ . What is the probability that $\angle APB$ is obtuse?

$\text{(A) }\frac {1}{5} \qquad \text{(B) }\frac {1}{4} \qquad \text{(C) }\frac {5}{16} \qquad \text{(D) }\frac {3}{8} \qquad \text{(E) }\frac {1}{2}$

Solution

Problem 18

A circle centered at $A$ with a radius of 1 and a circle centered at $B$ with a radius of 4 are externally tangent. A third circle is tangent to the first two and to one of their common external tangents as shown. The radius of the third circle is

$[asy] unitsize(0.75cm); pair A=(0,1), B=(4,4); dot(A); dot(B); draw( circle(A,1) ); draw( circle(B,4) ); draw( (-1.5,0)--(8.5,0) ); draw( A -- (A+(-1,0)) ); label("$1$", A -- (A+(-1,0)), N ); draw( B -- (B+(4,0)) ); label("$4$", B -- (B+(4,0)), N ); label("$A$",A,E); label("$B$",B,W); filldraw( circle( (12/9,4/9), 4/9 ), lightgray, black ); dot( (12/9,4/9) ); [/asy]$

$\text{(A) }\frac {1}{3} \qquad \text{(B) }\frac {2}{5} \qquad \text{(C) }\frac {5}{12} \qquad \text{(D) }\frac {4}{9} \qquad \text{(E) }\frac {1}{2}$

Solution

Problem 19

The polynomial $P(x)=x^3+ax^2+bx+c$ has the property that the mean of its zeros, the product of its zeros, and the sum of its coefficients are all equal. If the $y$ -intercept of the graph of $y=P(x)$ is 2, what is $b$ ?

$\text{(A) }-11 \qquad \text{(B) }-10 \qquad \text{(C) }-9 \qquad \text{(D) }1 \qquad \text{(E) }5$

Solution

Problem 20

Points $A = (3,9)$ , $B = (1,1)$ , $C = (5,3)$ , and $D=(a,b)$ lie in the first quadrant and are the vertices of quadrilateral $ABCD$ . The quadrilateral formed by joining the midpoints of $\overline{AB}$ , $\overline{BC}$ , $\overline{CD}$ , and $\overline{DA}$ is a square. What is the sum of the coordinates of point $D$ ?

$\text{(A) }7 \qquad \text{(B) }9 \qquad \text{(C) }10 \qquad \text{(D) }12 \qquad \text{(E) }16$

Solution

Problem 21

Four positive integers $a$ , $b$ , $c$ , and $d$ have a product of $8!$ and satisfy:

$\begin{align*} ab + a + b & = 524 \\ bc + b + c & = 146 \\ cd + c + d & = 104 \end{align*}$

What is $a-d$ ?

$\text{(A) }4 \qquad \text{(B) }6 \qquad \text{(C) }8 \qquad \text{(D) }10 \qquad \text{(E) }12$

Solution

Problem 22

In rectangle $ABCD$ , points $F$ and $G$ lie on $AB$ so that $AF=FG=GB$ and $E$ is the midpoint of $\overline{DC}$ . Also, $\overline{AC}$ intersects $\overline{EF}$ at $H$ and $\overline{EG}$ at $J$ . The area of the rectangle $ABCD$ is $70$ . Find the area of triangle $EHJ$ .

$\text{(A) }\frac {5}{2} \qquad \text{(B) }\frac {35}{12} \qquad \text{(C) }3 \qquad \text{(D) }\frac {7}{2} \qquad \text{(E) }\frac {35}{8}$

Solution

Problem 23

A polynomial of degree four with leading coefficient 1 and integer coefficients has two real zeros, both of which are integers. Which of the following can also be a zero of the polynomial?

$\text{(A) }\frac {1 + i \sqrt {11}}{2} \qquad \text{(B) }\frac {1 + i}{2} \qquad \text{(C) }\frac {1}{2} + i \qquad \text{(D) }1 + \frac {i}{2} \qquad \text{(E) }\frac {1 + i \sqrt {13}}{2}$

Solution

Problem 24

In $\triangle ABC$ , $\angle ABC=45^\circ$ . Point $D$ is on $\overline{BC}$ so that $2\cdot BD=CD$ and $\angle DAB=15^\circ$ . Find $\angle ACB$ .

$\text{(A) }54^\circ \qquad \text{(B) }60^\circ \qquad \text{(C) }72^\circ \qquad \text{(D) }75^\circ \qquad \text{(E) }90^\circ$

Solution

Problem 25

Consider sequences of positive real numbers of the form $x, 2000, y, \dots$ in which every term after the first is 1 less than the product of its two immediate neighbors. For how many different values of $x$ does the term $2001$ appear somewhere in the sequence?

$\text{(A) }1 \qquad \text{(B) }2 \qquad \text{(C) }3 \qquad \text{(D) }4 \qquad \text{(E) more than }4$

Solution

2001 AMC 12 (Problems • Answer Key • Resources)
Preceded by 2000 AMC 12 Problems	Followed by 2002 AMC 12A Problems
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Difference between revisions of "2001 AMC 12 Problems"

Latest revision as of 11:53, 24 January 2024

Contents

Problem 1

Problem 2

Problem 3

Problem 4

Problem 5

Problem 6

Problem 7

Problem 8

Problem 9

Problem 10

Problem 11

Problem 12

Problem 13

Problem 14

Problem 15

Problem 16

Problem 17

Problem 18

Problem 19

Problem 20

Problem 21

Problem 22

Problem 23

Problem 24

Problem 25

See also

@@ Line 1: / Line 1: @@
+{{AMC12 Problems|year=2001|ab=}}
 == Problem 1 ==
 The sum of two numbers is <math>S</math>. Suppose <math>3</math> is added to each number and then
@@ Line 9: / Line 10: @@
 == Problem 2 ==
+Let <math>P(n)</math> and <math>S(n)</math> denote the product and the sum, respectively, of the digits
+of the integer <math>n</math>. For example, <math>P(23) = 6</math> and <math>S(23) = 5</math>. Suppose <math>N</math> is a
+two-digit number such that <math>N = P(N)+S(N)</math>. What is the units digit of <math>N</math>?
+<math>\text{(A)}\ 2\qquad \text{(B)}\ 3\qquad \text{(C)}\ 6\qquad \text{(D)}\ 8\qquad \text{(E)}\ 9</math>
 [[2001 AMC 12 Problems/Problem 2|Solution]]
 == Problem 3 ==
+The state income tax where Kristin lives is levied at the rate of <math>p\%</math> of the first
+<math>\textdollar 28000</math> of annual income plus <math>(p + 2)\%</math> of any amount above <math>\textdollar 28000</math>. Kristin
+noticed that the state income tax she paid amounted to <math>(p + 0.25)\%</math> of her
+annual income. What was her annual income?
+<math>\text{(A)}\ \$28000\qquad \text{(B)}\ \$32000\qquad \text{(C)}\ \$35000\qquad \text{(D)}\ \$42000\qquad \text{(E)}\ \$56000</math>
 [[2001 AMC 12 Problems/Problem 3|Solution]]
 == Problem 4 ==
+The mean of three numbers is <math>10</math> more than the least of the numbers and <math>15</math>
+less than the greatest. The median of the three numbers is <math>5</math>. What is their
+sum?
+<math>\text{(A)}\ 5\qquad \text{(B)}\ 20\qquad \text{(C)}\ 25\qquad \text{(D)}\ 30\qquad \text{(E)}\ 36</math>
 [[2001 AMC 12 Problems/Problem 4|Solution]]
 == Problem 5 ==
+What is the product of all positive odd integers less than 10000?
+<math>\text{(A)}\ \dfrac{10000!}{(5000!)^2}\qquad \text{(B)}\ \dfrac{10000!}{2^{5000}}\qquad
+\text{(C)}\ \dfrac{9999!}{2^{5000}}\qquad \text{(D)}\ \dfrac{10000!}{2^{5000} \cdot 5000!}\qquad
+\text{(E)}\ \dfrac{5000!}{2^{5000}}</math>
 [[2001 AMC 12 Problems/Problem 5|Solution]]
 == Problem 6 ==
+A telephone number has the form <math>\text{ABC-DEF-GHIJ}</math>, where each letter represents
+a different digit. The digits in each part of the number are in decreasing
+order; that is, <math>A > B > C</math>, <math>D > E > F</math>, and <math>G > H > I > J</math>. Furthermore,
+<math>D</math>, <math>E</math>, and <math>F</math> are consecutive even digits; <math>G</math>, <math>H</math>, <math>I</math>, and <math>J</math> are consecutive odd
+digits; and <math>A + B + C = 9</math>. Find <math>A</math>.
+<math>\text{(A)}\ 4\qquad \text{(B)}\ 5\qquad \text{(C)}\ 6\qquad \text{(D)}\ 7\qquad \text{(E)}\ 8</math>
 [[2001 AMC 12 Problems/Problem 6|Solution]]
 == Problem 7 ==
+A charity sells <math>140</math> benefit tickets for a total of <math>\textdollar 2001</math>. Some tickets sell for full price (a whole dollar amount), and the rest sells for half price. How much money is raised by the full-price tickets?
+<math>\text{(A) }\$782\qquad \text{(B) }\$986\qquad \text{(C) }\$1158\qquad \text{(D) }\$1219\qquad \text{(E) }\$1449</math>
 [[2001 AMC 12 Problems/Problem 7|Solution]]
 == Problem 8 ==
+Which of the cones listed below can be formed from a <math>252^\circ</math> sector of a circle of radius <math>10</math> by aligning the two straight sides?
+<asy>
+import graph;
+unitsize(1.5cm);
+defaultpen(fontsize(8pt));
+draw(Arc((0,0),1,-72,180),linewidth(.8pt));
+draw(dir(288)--(0,0)--(-1,0),linewidth(.8pt));
+label("$10$",(-0.5,0),S);
+draw(Arc((0,0),0.1,-72,180));
+label("$252^{\circ}$",(0.05,0.05),NE);
+</asy>
+<math>\text{(A) A cone with slant height of } 10 \text{ and radius } 6</math>
+<math>\text{(B) A cone with height of } 10 \text{ and radius } 6</math>
+<math>\text{(C) A cone with slant height of } 10 \text{ and radius } 7</math>
+<math>\text{(D) A cone with height of } 10 \text{ and radius } 7</math>
+<math>\text{(E) A cone with slant height of } 10 \text{ and radius } 8</math>
 [[2001 AMC 12 Problems/Problem 8|Solution]]
 == Problem 9 ==
+Let <math>f</math> be a function satisfying <math>f(xy) = \frac{f(x)}y</math> for all positive real numbers <math>x</math> and <math>y</math>. If <math>f(500) =3</math>, what is the value of <math>f(600)</math>?
+<math>\text{(A)}\ 1 \qquad \text{(B)}\ 2 \qquad \text{(C)}\ \frac52 \qquad \text{(D)}\ 3 \qquad \text{(E)}\ \frac{18}5</math>
 [[2001 AMC 12 Problems/Problem 9|Solution]]
 == Problem 10 ==
+The plane is tiled by congruent squares and congruent pentagons as indicated. The percent of the plane that is enclosed by the pentagons is closest to
+<math>
+\text{(A) }50
+\qquad
+\text{(B) }52
+\qquad
+\text{(C) }54
+\qquad
+\text{(D) }56
+\qquad
+\text{(E) }58
+</math>
+<asy>
+unitsize(3mm);
+defaultpen(linewidth(0.8pt));
+path p1=(0,0)--(3,0)--(3,3)--(0,3)--(0,0);
+path p2=(0,1)--(1,1)--(1,0);
+path p3=(2,0)--(2,1)--(3,1);
+path p4=(3,2)--(2,2)--(2,3);
+path p5=(1,3)--(1,2)--(0,2);
+path p6=(1,1)--(2,2);
+path p7=(2,1)--(1,2);
+path[] p=p1^^p2^^p3^^p4^^p5^^p6^^p7;
+for(int i=0; i<3; ++i)
+{
+for(int j=0; j<3; ++j)
+{
+draw(shift(3*i,3*j)*p);
+}
+}
+</asy>
 [[2001 AMC 12 Problems/Problem 10|Solution]]
 == Problem 11 ==
+A box contains exactly five chips, three red and two white. Chips are randomly removed one at a time without replacement until all the red chips are drawn or all the white chips are drawn. What is the probability that the last chip drawn is white?
+<math>
+\text{(A) }\frac {3}{10}
+\qquad
+\text{(B) }\frac {2}{5}
+\qquad
+\text{(C) }\frac {1}{2}
+\qquad
+\text{(D) }\frac {3}{5}
+\qquad
+\text{(E) }\frac {7}{10}
+</math>
 [[2001 AMC 12 Problems/Problem 11|Solution]]
 == Problem 12 ==
+How many positive integers not exceeding <math>2001</math> are multiples of <math>3</math> or <math>4</math> but not <math>5</math>?
+<math>
+\text{(A) }768
+\qquad
+\text{(B) }801
+\qquad
+\text{(C) }934
+\qquad
+\text{(D) }1067
+\qquad
+\text{(E) }1167
+</math>
 [[2001 AMC 12 Problems/Problem 12|Solution]]
 == Problem 13 ==
+The parabola with equation <math>y=ax^2+bx+c</math> and vertex <math>(h,k)</math> is reflected about the line <math>y=k</math>. This results in the parabola with equation <math>y=dx^2+ex+f</math>. Which of the following equals <math>a+b+c+d+e+f</math>?
+<math>
+\text{(A) }2b
+\qquad
+\text{(B) }2c
+\qquad
+\text{(C) }2a+2b
+\qquad
+\text{(D) }2h
+\qquad
+\text{(E) }2k
+</math>
 [[2001 AMC 12 Problems/Problem 13|Solution]]
 == Problem 14 ==
+Given the nine-sided regular polygon <math>A_1 A_2 A_3 A_4 A_5 A_6 A_7 A_8 A_9</math>, how many distinct equilateral triangles in the plane of the polygon have at least two vertices in the set <math>\{A_1,A_2,\dots,A_9\}</math>?
+<math>
+\text{(A) }30
+\qquad
+\text{(B) }36
+\qquad
+\text{(C) }63
+\qquad
+\text{(D) }66
+\qquad
+\text{(E) }72
+</math>
 [[2001 AMC 12 Problems/Problem 14|Solution]]
 == Problem 15 ==
+An insect lives on the surface of a regular tetrahedron with edges of length 1. It wishes to travel on the surface of the tetrahedron from the midpoint of one edge to the midpoint of the opposite edge. What is the length of the shortest such trip? (Note: Two edges of a tetrahedron are opposite if they have no common endpoint.)
+<math>
+\text{(A) }\frac {1}{2} \sqrt {3}
+\qquad
+\text{(B) }1
+\qquad
+\text{(C) }\sqrt {2}
+\qquad
+\text{(D) }\frac {3}{2}
+\qquad
+\text{(E) }2
+</math>
 [[2001 AMC 12 Problems/Problem 15|Solution]]
 == Problem 16 ==
+A spider has one sock and one shoe for each of its eight legs. In how many different orders can the spider put on its socks and shoes, assuming that, on each leg, the sock must be put on before the shoe?
+<math>
+\text{(A) }8!
+\qquad
+\text{(B) }2^8 \cdot 8!
+\qquad
+\text{(C) }(8!)^2
+\qquad
+\text{(D) }\frac {16!}{2^8}
+\qquad
+\text{(E) }16!
+</math>
 [[2001 AMC 12 Problems/Problem 16|Solution]]
 == Problem 17 ==
+A point <math>P</math> is selected at random from the interior of the pentagon with vertices <math>A = (0,2)</math>, <math>B = (4,0)</math>, <math>C = (2 \pi + 1, 0)</math>, <math>D = (2 \pi + 1,4)</math>, and <math>E=(0,4)</math>. What is the probability that <math>\angle APB</math> is obtuse?
+<math>
+\text{(A) }\frac {1}{5}
+\qquad
+\text{(B) }\frac {1}{4}
+\qquad
+\text{(C) }\frac {5}{16}
+\qquad
+\text{(D) }\frac {3}{8}
+\qquad
+\text{(E) }\frac {1}{2}
+</math>
 [[2001 AMC 12 Problems/Problem 17|Solution]]
 == Problem 18 ==
+A circle centered at <math>A</math> with a radius of 1 and a circle centered at <math>B</math> with a radius of 4 are externally tangent. A third circle is tangent to the first two and to one of their common external tangents as shown. The radius of the third circle is
+<asy>
+unitsize(0.75cm);
+pair A=(0,1), B=(4,4);
+dot(A); dot(B);
+draw( circle(A,1) );
+draw( circle(B,4) );
+draw( (-1.5,0)--(8.5,0) );
+draw( A -- (A+(-1,0)) );
+label("$1$", A -- (A+(-1,0)), N );
+draw( B -- (B+(4,0)) );
+label("$4$", B -- (B+(4,0)), N );
+label("$A$",A,E);
+label("$B$",B,W);
+filldraw( circle( (12/9,4/9), 4/9 ), lightgray, black );
+dot( (12/9,4/9) );
+</asy>
+<math>
+\text{(A) }\frac {1}{3}
+\qquad
+\text{(B) }\frac {2}{5}
+\qquad
+\text{(C) }\frac {5}{12}
+\qquad
+\text{(D) }\frac {4}{9}
+\qquad
+\text{(E) }\frac {1}{2}
+</math>
 [[2001 AMC 12 Problems/Problem 18|Solution]]
 == Problem 19 ==
+The polynomial <math>P(x)=x^3+ax^2+bx+c</math> has the property that the mean of its zeros, the product of its zeros, and the sum of its coefficients are all equal. If the <math>y</math>-intercept of the graph of <math>y=P(x)</math> is 2, what is <math>b</math>?
+<math>
+\text{(A) }-11
+\qquad
+\text{(B) }-10
+\qquad
+\text{(C) }-9
+\qquad
+\text{(D) }1
+\qquad
+\text{(E) }5
+</math>
 [[2001 AMC 12 Problems/Problem 19|Solution]]
 == Problem 20 ==
+Points <math>A = (3,9)</math>, <math>B = (1,1)</math>, <math>C = (5,3)</math>, and <math>D=(a,b)</math> lie in the first quadrant and are the vertices of quadrilateral <math>ABCD</math>. The quadrilateral formed by joining the midpoints of <math>\overline{AB}</math>, <math>\overline{BC}</math>, <math>\overline{CD}</math>, and <math>\overline{DA}</math> is a square. What is the sum of the coordinates of point <math>D</math>?
+<math>
+\text{(A) }7
+\qquad
+\text{(B) }9
+\qquad
+\text{(C) }10
+\qquad
+\text{(D) }12
+\qquad
+\text{(E) }16
+</math>
 [[2001 AMC 12 Problems/Problem 20|Solution]]
 == Problem 21 ==
+Four positive integers <math>a</math>, <math>b</math>, <math>c</math>, and <math>d</math> have a product of <math>8!</math> and satisfy:
+<cmath>
+\begin{align*}
+ab + a + b & = 524
+\\
+bc + b + c & = 146
+\\
+cd + c + d & = 104
+\end{align*}
+</cmath>
+What is <math>a-d</math>?
+<math>
+\text{(A) }4
+\qquad
+\text{(B) }6
+\qquad
+\text{(C) }8
+\qquad
+\text{(D) }10
+\qquad
+\text{(E) }12
+</math>
 [[2001 AMC 12 Problems/Problem 21|Solution]]
 == Problem 22 ==
+In rectangle <math>ABCD</math>, points <math>F</math> and <math>G</math> lie on <math>AB</math> so that <math>AF=FG=GB</math> and <math>E</math> is the midpoint of <math>\overline{DC}</math>. Also, <math>\overline{AC}</math> intersects <math>\overline{EF}</math> at <math>H</math> and <math>\overline{EG}</math> at <math>J</math>. The area of the rectangle <math>ABCD</math> is <math>70</math>. Find the area of triangle <math>EHJ</math>.
+<math>
+\text{(A) }\frac {5}{2}
+\qquad
+\text{(B) }\frac {35}{12}
+\qquad
+\text{(C) }3
+\qquad
+\text{(D) }\frac {7}{2}
+\qquad
+\text{(E) }\frac {35}{8}
+</math>
 [[2001 AMC 12 Problems/Problem 22|Solution]]
 == Problem 23 ==
+A polynomial of degree four with leading coefficient 1 and integer coefficients has two real zeros, both of which are integers. Which of the following can also be a zero of the polynomial?
+<math>
+\text{(A) }\frac {1 + i \sqrt {11}}{2}
+\qquad
+\text{(B) }\frac {1 + i}{2}
+\qquad
+\text{(C) }\frac {1}{2} + i
+\qquad
+\text{(D) }1 + \frac {i}{2}
+\qquad
+\text{(E) }\frac {1 + i \sqrt {13}}{2}
+</math>
 [[2001 AMC 12 Problems/Problem 23|Solution]]
 == Problem 24 ==
+In <math>\triangle ABC</math>, <math>\angle ABC=45^\circ</math>. Point <math>D</math> is on <math>\overline{BC}</math> so that <math>2\cdot BD=CD</math> and <math>\angle DAB=15^\circ</math>. Find <math>\angle ACB</math>.
+<math>
+\text{(A) }54^\circ
+\qquad
+\text{(B) }60^\circ
+\qquad
+\text{(C) }72^\circ
+\qquad
+\text{(D) }75^\circ
+\qquad
+\text{(E) }90^\circ
+</math>
 [[2001 AMC 12 Problems/Problem 24|Solution]]
 == Problem 25 ==
+Consider sequences of positive real numbers of the form <math>x, 2000, y, \dots</math> in which every term after the first is 1 less than the product of its two immediate neighbors. For how many different values of <math>x</math> does the term <math>2001</math> appear somewhere in the sequence?
+<math>
+\text{(A) }1
+\qquad
+\text{(B) }2
+\qquad
+\text{(C) }3
+\qquad
+\text{(D) }4
+\qquad
+\text{(E) more than }4
+</math>
 [[2001 AMC 12 Problems/Problem 25|Solution]]
 == See also ==
+{{AMC12 box|year=2001|before=[[2000 AMC 12 Problems]]|after=[[2002 AMC 12A Problems]]}}
 * [[AMC 12]]
 * [[AMC 12 Problems and Solutions]]
 * [[2001 AMC 12]]
 * [[Mathematics competition resources]]
+{{MAA Notice}}