Difference between revisions of "2012 AMC 12B Problems"
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[[2012 AMC 12B Problems/Problem 1|Solution]] | [[2012 AMC 12B Problems/Problem 1|Solution]] | ||
+ | |||
+ | == Problem 2 == | ||
+ | |||
+ | A circle of radius 5 is inscribed in a rectangle as shown. The ratio of the length of the rectangle to its width is 2:1. What is the area of the rectangle? | ||
+ | |||
+ | <math>\textbf{(A)}\ 50\qquad\textbf{(B)}\ 100\qquad\textbf{(C)}\ 125\qquad\textbf{(D)}\ 150\qquad\textbf{(E)}\ 200</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 2|Solution]] | ||
+ | |||
+ | == Problem 3 == | ||
+ | |||
+ | For a science project, Sammy observed a chipmunk and squirrel stashing acorns in holes. The chipmunk hid 3 acorns in each of the holes it dug. The squirrel hid 4 acorns in each of the holes it dug. They each hid the same number of acorns, although the squirrel needed 4 fewer holes. How many acorns did the chipmunk hide? | ||
+ | |||
+ | <math>\textbf{(A)}\ 30\qquad\textbf{(B)}\ 36\qquad\textbf{(C)}\ 42\qquad\textbf{(D)}\ 48\qquad\textbf{(E)}\ 54</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 3|Solution]] | ||
+ | |||
+ | == Problem 4 == | ||
+ | |||
+ | Suppose that the euro is worth 1.30 dollars. If Diana has 500 dollars and Etienne has 400 euros, by what percent is the value of Etienne's money greater that the value of Diana's money? | ||
+ | |||
+ | <math>\textbf{(A)}\ 2\qquad\textbf{(B)}\ 4\qquad\textbf{(C)}\ 6.5\qquad\textbf{(D)}\ 8\qquad\textbf{(E)}\ 13</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 4|Solution]] | ||
+ | |||
+ | == Problem 5 == | ||
+ | |||
+ | Two integers have a sum of 26. when two more integers are added to the first two, the sum is 41. Finally, when two more integers are added to the sum of the previous 4 integers, the sum is 57. What is the minimum number of even integers among the 6 integers? | ||
+ | |||
+ | <math>\textbf{(A)}\ 1\qquad\textbf{(B)}\ 2\qquad\textbf{(C)}\ 3\qquad\textbf{(D)}\ 4\qquad\textbf{(E)}\ 5</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 5|Solution]] | ||
+ | |||
+ | == Problem 6 == | ||
+ | |||
+ | In order to estimate the value of <math>x-y</math> where <math>x</math> and <math>y</math> are real numbers with <math>x > y > 0</math>, Xiaoli rounded <math>x</math> up by a small amount, rounded <math>y</math> down by the same amount, and then subtracted her rounded values. Which of the following statements is necessarily correct? | ||
+ | |||
+ | <math>\textbf{(A)}\ \text{Her estimate is larger than }x-y</math> | ||
+ | |||
+ | <math>\textbf{(B)}\ \text{Her estimate is smaller than }x-y</math> | ||
+ | |||
+ | <math>\textbf{(C)}\ \text{Her estimate equals }x-y</math> | ||
+ | |||
+ | <math>\textbf{(D)}\ \text{Her estimate equals }y - x</math> | ||
+ | |||
+ | <math>\textbf{(E)}\ \text{Her estimate is 0}</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 6|Solution]] | ||
+ | |||
+ | == Problem 7 == | ||
+ | |||
+ | Small lights are hung on a string 6 inches apart in the order red, red, green, green, green, red, red, green, green, green, and so on continuing this pattern of 2 red lights followed by 3 green lights. How many feet separate the 3rd red light and the 21st red light? | ||
+ | |||
+ | '''Note:''' 1 foot is equal to 12 inches. | ||
+ | |||
+ | <math>\textbf{(A)}\ 18\qquad\textbf{(B)}\ 18.5\qquad\textbf{(C)}\ 20\qquad\textbf{(D)}\ 20.5\qquad\textbf{(E)}\ 22.5 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 7|Solution]] | ||
+ | |||
+ | == Problem 8 == | ||
+ | |||
+ | A dessert chef prepares the dessert for every day of a week starting with Sunday. The dessert each day is either cake, pie, ice cream, or pudding. The same dessert may not be served two days in a row. There must be cake on Friday because of a birthday. How many different dessert menus for the week are possible? | ||
+ | |||
+ | <math>\textbf{(A)}\ 729\qquad\textbf{(B)}\ 972\qquad\textbf{(C)}\ 1024\qquad\textbf{(D)}\ 2187\qquad\textbf{(E)}\ 2304 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 8|Solution]] | ||
+ | |||
+ | == Problem 9 == | ||
+ | |||
+ | It takes Clea 60 seconds to walk down an escalator when it is not moving, and 24 seconds when it is moving. How seconds would it take Clea to ride the escalator down when she is not walking? | ||
+ | |||
+ | <math>\textbf{(A)}\ 36\qquad\textbf{(B)}\ 40\qquad\textbf{(C)}\ 42\qquad\textbf{(D)}\ 48\qquad\textbf{(E)}\ 52 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 9|Solution]] | ||
+ | |||
+ | == Problem 10 == | ||
+ | |||
+ | What is the area of the polygon whose vertices are the points of intersection of the curves <math>x^2 + y^2 =25</math> and <math>(x-4)^2 + 9y^2 = 81</math>? | ||
+ | |||
+ | <math>\textbf{(A)}\ 24\qquad\textbf{(B)}\ 27\qquad\textbf{(C)}\ 36\qquad\textbf{(D)}\ 37.5\qquad\textbf{(E)}\ 42</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 10|Solution]] | ||
+ | |||
+ | == Problem 11 == | ||
+ | |||
+ | In the equation below, <math>A</math> and <math>B</math> are consecutive positive integers, and <math>A</math>, <math>B</math>, and <math>A+B</math> represent number bases: <cmath>132_A+43_B=69_{A+B}.</cmath> | ||
+ | What is <math>A+B</math>? | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 11|Solution]] | ||
+ | |||
+ | <math>\textbf{(A)}\ 9\qquad\textbf{(B)}\ 11\qquad\textbf{(C)}\ 13\qquad\textbf{(D)}\ 15\qquad\textbf{(E)}\ 17 </math> | ||
+ | |||
+ | == Problem 12 == | ||
+ | |||
+ | How many sequences of zeros and ones of length 20 have all thte zeros consecutive, or all the ones consecutive, or both? | ||
+ | |||
+ | <math>\textbf{(A)}\ 190\qquad\textbf{(B)}\ 192\qquad\textbf{(C)}\ 211\qquad\textbf{(D)}\ 380\qquad\textbf{(E)}\ 382 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 12|Solution]] | ||
+ | |||
+ | == Problem 13 == | ||
+ | |||
+ | Two parabolas have equations <math>y= x^2 + ax +b</math> and <math>y= x^2 + cx +d</math>, where <math>a</math>, <math>b</math>, <math>c</math>, and <math>d</math> are integers, each chosen independently by rolling a fair six-sided die. What is the probability that the parabolas will have a least one point in common? | ||
+ | |||
+ | <math>\textbf{(A)}\ \frac{1}{2}\qquad\textbf{(B)}\ \frac{25}{36}\qquad\textbf{(C)}\ \frac{5}{6}\qquad\textbf{(D)}\ \frac{31}{36}\qquad\textbf{(E)}\ 1 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 13|Solution]] | ||
== Problem 14 == | == Problem 14 == | ||
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[[2012 AMC 12B Problems/Problem 14|Solution]] | [[2012 AMC 12B Problems/Problem 14|Solution]] | ||
+ | |||
+ | == Problem 15 == | ||
+ | |||
+ | Jesse cuts a circular paper disk of radius 12 along two radii to form two sectors, the smaller having a central angle of 120 degrees. He makes two circular cones, using each sector to form the lateral surface of a cone. What is the ratio of the volume of the smaller cone to that of the larger? | ||
+ | |||
+ | <math>\textbf{(A)}\ \frac{1}{8}\qquad\textbf{(B)}\ \frac{1}{4}\qquad\textbf{(C)}\ \frac{\sqrt{10}}{10}\qquad\textbf{(D)}\ \frac{\sqrt{5}}{6}\qquad\textbf{(E)}\ \frac{\sqrt{5}}{5}</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 15|Solution]] | ||
+ | |||
+ | == Problem 16 == | ||
+ | |||
+ | Amy, Beth, and Jo listen to four different songs and discuss which ones they like. No song is liked by all three. Furthermore, for each of the three pairs of the girls, there is at least one song liked by those girls but disliked by the third. In how many different ways is this possible? | ||
+ | |||
+ | <math>\textbf{(A)}\ 108\qquad\textbf{(B)}\ 132\qquad\textbf{(C)}\ 671\qquad\textbf{(D)}\ 846\qquad\textbf{(E)}\ 1105 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 16|Solution]] | ||
+ | |||
+ | == Problem 17 == | ||
+ | |||
+ | Square <math>PQRS</math> lies in the first quadrant. Points <math>(3,0), (5,0), (7,0),</math> and <math>(13,0)</math> lie on lines <math>SP, RQ, PQ,</math> and <math>SR</math>, respectively. What is the sum of the coordinates of the center of the square <math>PQRS</math>? | ||
+ | |||
+ | <math>\textbf{(A)}\ 6\qquad\textbf{(B)}\ 6.2\qquad\textbf{(C)}\ 6.4\qquad\textbf{(D)}\ 6.6\qquad\textbf{(E)}\ 6.8 </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 17|Solution]] | ||
+ | |||
+ | == Problem 18 == | ||
+ | |||
+ | Let <math>(a_1,a_2, \dots ,a_{10})</math> be a list of the first 10 positive integers such that for each <math>2 \le i \le 10</math> either <math>a_i+1</math> or <math>a_i-1</math> or both appear somewhere before <math>a_i</math> in the list. How many such lists are there? | ||
+ | |||
+ | <math>\textbf{(A)}\ 120\qquad\textbf{(B)}\ 512\qquad\textbf{(C)}\ 1024\qquad\textbf{(D)}\ 181,440\qquad\textbf{(E)}\ 362,880</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 18|Solution]] | ||
+ | |||
+ | == Problem 19 == | ||
+ | |||
+ | A unit cube has vertices <math>P_1,P_2,P_3,P_4,P_1',P_2',P_3',</math> and <math>P_4'</math>. Vertices <math>P_2</math>, <math>P_3</math>, and <math>P_4</math> are adjacent to <math>P_1</math>, and for <math>1\le i\le 4,</math> vertices <math>P_i</math> and <math>P_i'</math> are opposite to each other. A regular octahedron has one vertex in each of the segments <math>P_1P_2</math>, <math>P_1P_3</math>, <math>P_1P_4</math>, <math>P_1'P_2'</math>, <math>P_1'P_3'</math>, and <math>P_1'P_4'</math>. What is the octahedron's side length? | ||
+ | |||
+ | <math>\textbf{(A)}\ \frac{3\sqrt{2}}{4}\qquad\textbf{(B)}\ \frac{7\sqrt{6}}{16}\qquad\textbf{(C)}\ \frac{\sqrt{5}}{2}\qquad\textbf{(D)}\ \frac{2\sqrt{3}}{3}\qquad\textbf{(E)}\ \frac{\sqrt{6}}{2} </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 19|Solution]] | ||
+ | |||
+ | == Problem 20 == | ||
+ | |||
+ | A trapezoid has side lengths 3, 5, 7, and 11. The sums of all the possible areas of the trapezoid can be written in the form of <math>r_1\sqrt{n_1}+r_2\sqrt{n_2}+r_3</math>, where <math>r_1</math>, <math>r_2</math>, and <math>r_3</math> are rational numbers and <math>n_1</math> and <math>n_2</math> are positive integers not divisible by the square of any prime. What is the greatest integer less than or equal to <math>r_1+r_2+r_3+n_1+n_2</math>? | ||
+ | |||
+ | <math>\textbf{(A)}\ 57\qquad\textbf{(B)}\ 59\qquad\textbf{(C)}\ 61\qquad\textbf{(D)}\ 63\qquad\textbf{(E)}\ 65</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 20|Solution]] | ||
+ | |||
+ | == Problem 21 == | ||
+ | |||
+ | Square <math>AXYZ</math> is inscribed in equiangular hexagon <math>ABCDEF</math> with <math>X</math> on <math>\overline{BC}</math>, <math>Y</math> on <math>\overline{DE}</math>, and <math>Z</math> on <math>\overline{EF}</math>. Suppose that <math>AB=40</math>, and <math>EF=41(\sqrt{3}-1)</math>. What is the side-length of the square? | ||
+ | |||
+ | <math>\textbf{(A)}\ 29\sqrt{3} \qquad\textbf{(B)}\ \frac{21}{2}\sqrt{2}+\frac{41}{2}\sqrt{3}\qquad\textbf{(C)}\ 20\sqrt{3}+16</math> | ||
+ | |||
+ | <math>\textbf{(D)}\ 20\sqrt{2}+13\sqrt{3} \qquad\textbf{(E)}\ 21\sqrt{6} </math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 21|Solution]] | ||
+ | |||
+ | == Problem 22 == | ||
+ | |||
+ | A bug travels from <math>A</math> to <math>B</math> along the segments in the hexagonal lattice pictured below. The segments marked with an arrow can be traveled only in the direction of the arrow, and the bug never travels the same segment more than once. How many different paths are there? | ||
+ | |||
+ | <math>\textbf{(A)}\ 2112\qquad\textbf{(B)}\ 2304\qquad\textbf{(C)}\ 2368\qquad\textbf{(D)}\ 2384\qquad\textbf{(E)}\ 2400</math> | ||
+ | |||
+ | [[2012 AMC 12B Problems/Problem 22|Solution]] |
Revision as of 23:41, 24 February 2012
2012 AMC 12B (Answer Key) Printable version: | AoPS Resources • PDF | ||
Instructions
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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 |
Contents
Problem 1
Each third-grade classroom at Pearl Creek Elementary has 18 students and 2 pet rabbits. How many more students than rabbits are there in all 4 of the third-grade classrooms?
Problem 2
A circle of radius 5 is inscribed in a rectangle as shown. The ratio of the length of the rectangle to its width is 2:1. What is the area of the rectangle?
Problem 3
For a science project, Sammy observed a chipmunk and squirrel stashing acorns in holes. The chipmunk hid 3 acorns in each of the holes it dug. The squirrel hid 4 acorns in each of the holes it dug. They each hid the same number of acorns, although the squirrel needed 4 fewer holes. How many acorns did the chipmunk hide?
Problem 4
Suppose that the euro is worth 1.30 dollars. If Diana has 500 dollars and Etienne has 400 euros, by what percent is the value of Etienne's money greater that the value of Diana's money?
Problem 5
Two integers have a sum of 26. when two more integers are added to the first two, the sum is 41. Finally, when two more integers are added to the sum of the previous 4 integers, the sum is 57. What is the minimum number of even integers among the 6 integers?
Problem 6
In order to estimate the value of where and are real numbers with , Xiaoli rounded up by a small amount, rounded down by the same amount, and then subtracted her rounded values. Which of the following statements is necessarily correct?
Problem 7
Small lights are hung on a string 6 inches apart in the order red, red, green, green, green, red, red, green, green, green, and so on continuing this pattern of 2 red lights followed by 3 green lights. How many feet separate the 3rd red light and the 21st red light?
Note: 1 foot is equal to 12 inches.
Problem 8
A dessert chef prepares the dessert for every day of a week starting with Sunday. The dessert each day is either cake, pie, ice cream, or pudding. The same dessert may not be served two days in a row. There must be cake on Friday because of a birthday. How many different dessert menus for the week are possible?
Problem 9
It takes Clea 60 seconds to walk down an escalator when it is not moving, and 24 seconds when it is moving. How seconds would it take Clea to ride the escalator down when she is not walking?
Problem 10
What is the area of the polygon whose vertices are the points of intersection of the curves and ?
Problem 11
In the equation below, and are consecutive positive integers, and , , and represent number bases: What is ?
Problem 12
How many sequences of zeros and ones of length 20 have all thte zeros consecutive, or all the ones consecutive, or both?
Problem 13
Two parabolas have equations and , where , , , and are integers, each chosen independently by rolling a fair six-sided die. What is the probability that the parabolas will have a least one point in common?
Problem 14
Bernardo and Silvia play the following game. An integer between 0 and 999 inclusive is selected and given to Bernardo. Whenever Bernardo receives a number, he doubles it and passes the result to Silvia. Whenever Silvia receives a number, she addes 50 to it and passes the result to Bernardo. The winner is the last person who produces a number less than 1000. Let N be the smallest initial number that results in a win for Bernardo. What is the sum of the digits of N?
Problem 15
Jesse cuts a circular paper disk of radius 12 along two radii to form two sectors, the smaller having a central angle of 120 degrees. He makes two circular cones, using each sector to form the lateral surface of a cone. What is the ratio of the volume of the smaller cone to that of the larger?
Problem 16
Amy, Beth, and Jo listen to four different songs and discuss which ones they like. No song is liked by all three. Furthermore, for each of the three pairs of the girls, there is at least one song liked by those girls but disliked by the third. In how many different ways is this possible?
Problem 17
Square lies in the first quadrant. Points and lie on lines and , respectively. What is the sum of the coordinates of the center of the square ?
Problem 18
Let be a list of the first 10 positive integers such that for each either or or both appear somewhere before in the list. How many such lists are there?
Problem 19
A unit cube has vertices and . Vertices , , and are adjacent to , and for vertices and are opposite to each other. A regular octahedron has one vertex in each of the segments , , , , , and . What is the octahedron's side length?
Problem 20
A trapezoid has side lengths 3, 5, 7, and 11. The sums of all the possible areas of the trapezoid can be written in the form of , where , , and are rational numbers and and are positive integers not divisible by the square of any prime. What is the greatest integer less than or equal to ?
Problem 21
Square is inscribed in equiangular hexagon with on , on , and on . Suppose that , and . What is the side-length of the square?
Problem 22
A bug travels from to along the segments in the hexagonal lattice pictured below. The segments marked with an arrow can be traveled only in the direction of the arrow, and the bug never travels the same segment more than once. How many different paths are there?