Difference between revisions of "2005 AMC 12B Problems"
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== Problem 11 == | == Problem 11 == | ||
− | An envelope contains eight bills: <math>2</math> ones, <math>2</math> fives, <math>2</math> tens, and <math>2</math> twenties. Two bills are drawn at random without replacement. What is the probability that their sum is <math>20</math> or more? | + | An envelope contains eight bills: <math>2</math> ones, <math>2</math> fives, <math>2</math> tens, and <math>2</math> twenties. Two bills are drawn at random without replacement. What is the probability that their sum is $<math>20</math> or more? |
<math>\mathrm{(A)}\ {{{\frac{1}{4}}}} \qquad \mathrm{(B)}\ {{{\frac{2}{7}}}} \qquad \mathrm{(C)}\ {{{\frac{3}{7}}}} \qquad \mathrm{(D)}\ {{{\frac{1}{2}}}} \qquad \mathrm{(E)}\ {{{\frac{2}{3}}}}</math> | <math>\mathrm{(A)}\ {{{\frac{1}{4}}}} \qquad \mathrm{(B)}\ {{{\frac{2}{7}}}} \qquad \mathrm{(C)}\ {{{\frac{3}{7}}}} \qquad \mathrm{(D)}\ {{{\frac{1}{2}}}} \qquad \mathrm{(E)}\ {{{\frac{2}{3}}}}</math> |
Revision as of 17:47, 16 July 2011
Contents
- 1 Problem 1
- 2 Problem 2
- 3 Problem 3
- 4 Problem 4
- 5 Problem 5
- 6 Problem 6
- 7 Problem 7
- 8 Problem 8
- 9 Problem 9
- 10 Problem 10
- 11 Problem 11
- 12 Problem 12
- 13 Problem 13
- 14 Problem 14
- 15 Problem 15
- 16 Problem 16
- 17 Problem 17
- 18 Problem 18
- 19 Problem 19
- 20 Problem 20
- 21 Problem 21
- 22 Problem 22
- 23 Problem 23
- 24 Problem 24
- 25 Problem 25
- 26 See also
Problem 1
A scout troop buys candy bars at a price of five for
dollars. They sell all the candy bars at the price of two for
dollar. What was their profit, in dollars?
Problem 2
A positive number has the property that
of
is
. What is
?
Problem 3
Brianna is using part of the money she earned on her weekend job to buy several equally-priced CDs. She used one fifth of her money to buy one third of the CDs. What fraction of her money will she have left after she buys all the CDs?
Problem 4
At the beginning of the school year, Lisa's goal was to earn an A on at least of her
quizzes for the year. She earned an A on
of the first
quizzes. If she is to achieve her goal, on at most how many of the remaining quizzes can she earn a grade lower than an A?
Problem 5
An -foot by
-foot floor is tiles with square tiles of size
foot by
foot. Each tile has a pattern consisting of four white quarter circles of radius
foot centered at each corner of the tile. The remaining portion of the tile is shaded. How many square feet of the floor are shaded?
Problem 6
In , we have
and
. Suppose that
is a point on line
such that
lies between
and
and
. What is
?
Problem 7
What is the area enclosed by the graph of ?
Problem 8
For how many values of is it true that the line
passes through the
vertex of the parabola
?
Problem 9
On a certain math exam, of the students got
points,
got
points,
got
points,
got
points, and the rest got
points. What is the difference between the mean and the median score on this exam?
Problem 10
The first term of a sequence is . Each succeeding term is the sum of the cubes of the digits of the previous terms. What is the
term of the sequence?
Problem 11
An envelope contains eight bills: ones,
fives,
tens, and
twenties. Two bills are drawn at random without replacement. What is the probability that their sum is $
or more?
Problem 12
The quadratic equation has roots twice those of
, and none of
and
is zero. What is the value of
?
Problem 13
Suppose that ,
,
, ... ,
. What is
?
Problem 14
A circle having center , with
,is tangent to the lines
,
and
. What is the radius of this circle?
Problem 15
The sum of four two-digit numbers is . None of the eight digits is
and no two of them are the same. Which of the following is not included among the eight digits?
Problem 16
Eight spheres of radius 1, one per octant, are each tangent to the coordinate planes. What is the radius of the smallest sphere, centered at the origin, that contains these eight spheres?
Problem 17
How many distinct four-tuples of rational numbers are there with
?
Problem 18
Let and
be points in the plane. Define
as the region in the first quadrant consisting of those points
such that
is an acute triangle. What is the closest integer to the area of the region
?
Problem 19
Let and
be two-digit integers such that
is obtained by reversing the digits of
. The integers
and
satisfy
for some positive integer
. What is
?
Problem 20
Let and
be distinct elements in the set
What is the minimum possible value of
Problem 21
A positive integer has
divisors and
has
divisors. What is the greatest integer
such that
divides
?
Problem 22
A sequence of complex numbers is defined by the rule
where is the complex conjugate of
and
. Suppose that
and
. How many possible values are there for
?
Problem 23
Let be the set of ordered triples
of real numbers for which
There are real numbers
and
such that for all ordered triples
in
we have
What is the value of
Problem 24
All three vertices of an equilateral triangle are on the parabola , and one of its sides has a slope of
. The
-coordinates of the three vertices have a sum of
, where
and
are relatively prime positive integers. What is the value of
?
Problem 25
Six ants simultaneously stand on the six vertices of a regular octahedron, with each ant at a different vertex. Simultaneously and independently, each ant moves from its vertex to one of the four adjacent vertices, each with equal probability. What is the probability that no two ants arrive at the same vertex?