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AMC 12 2005 A

Question 1

Two is of and of . What is ?

Solution

  
  2020-07-09 06:38:46

Question 2

The equations and have the same solution. What is the value of ?

Solution

  
  2020-07-09 06:38:46

Question 3

A rectangle with diagonal length is twice as long as it is wide. What is the area of the rectangle?

Solution

  
  2020-07-09 06:38:46

Question 4

A store normally sells windows at each. This week the store is offering one free window for each purchase of four. Dave needs seven windows and Doug needs eight windows. How much will they save if they purchase the windows together rather than separately?

Solution

  
  2020-07-09 06:38:46

Question 5

The average (mean) of 20 numbers is 30, and the average of 30 other numbers is 20. What is the average of all 50 numbers?

Solution

  
  2020-07-09 06:38:46

Question 6

Josh and Mike live 13 miles apart. Yesterday, Josh started to ride his bicycle toward Mike's house. A little later Mike started to ride his bicycle toward Josh's house. When they met, Josh had ridden for twice the length of time as Mike and at four-fifths of Mike's rate. How many miles had Mike ridden when they met?

Solution

  
  2020-07-09 06:38:46

Question 7

Square is inside the square so that each side of can be extended to pass through a vertex of . Square has side length and . What is the area of the inner square ?

Solution

This is an easy question. All you need is to see triangle BEC is a right triangle. Then you can use the Pythagorean Theorem to figure out the side of inner square. Why is FC also 1?
  
jimmy  2016-09-16 15:06:03

Question 8

Let , and be digits with

What is ?

Solution

  
  2020-07-09 06:38:46

Question 9

There are two values of for which the equation has only one solution for . What is the sum of these values of ?

Solution

  
  2020-07-09 06:38:46

Question 10

A wooden cube units on a side is painted red on all six faces and then cut into unit cubes. Exactly one-fourth of the total number of faces of the unit cubes are red. What is ?

Solution

  
  2020-07-09 06:38:46

Question 11

How many three-digit numbers satisfy the property that the middle digit is the average of the first and the last digits?

Solution

  
  2020-07-09 06:38:46

Question 12

A line passes through and . How many other points with integer coordinates are on the line and strictly between and ?

Solution

  
  2020-07-09 06:38:46

Question 13

In the five-sided star shown, the letters , , , and are replaced by the numbers 3, 5, 6, 7 and 9, although not necessarily in that order. The sums of the numbers at the ends of the line segments , , , , and form an arithmetic sequence, although not necessarily in that order. What is the middle term of the arithmetic sequence?

Solution

This question will be simple if you remember the rule: in an arithmetic sequence:

median=mean

Sum of AB+BC+CD+DE+EA = 2(A+B+C+D+E) = 2*30 = 60
CD is middle of arithmetic sequence, so it must be average of the 5 numbers: so CD = 60/5 = 12
  
allenx123456  2016-12-20 19:30:00

Question 14

On a standard die one of the dots is removed at random with each dot equally likely to be chosen. The die is then rolled. What is the probability that the top face has an odd number of dots?

Solution

  
  2020-07-09 06:38:46

Question 15

Let be a diameter of a circle and be a point on with . Let and be points on the circle such that and is a second diameter. What is the ratio of the area of to the area of ?

Solution

  
  2020-07-09 06:38:46

Question 16

Three circles of radius are drawn in the first quadrant of the -plane. The first circle is tangent to both axes, the second is tangent to the first circle and the -axis, and the third is tangent to the first circle and the -axis. A circle of radius is tangent to both axes and to the second and third circles. What is ?

Solution

  
  2020-07-09 06:38:46

Question 17

A unit cube is cut twice to form three triangular prisms, two of which are congruent, as shown in Figure 1. The cube is then cut in the same manner along the dashed lines shown in Figure 2. This creates nine pieces. What is the volume of the piece that contains vertex ?

Solution

The piece that contains vertex W is a pyramid.

Pyramid volume = L*W*H / 3, where
L base length
W base width
H pyramid height
  
allenx123456  2016-12-20 19:30:56

Question 18

Call a number "prime-looking" if it is composite but not divisible by 2, 3, or 5. The three smallest prime-looking numbers are 49, 77, and 91. There are 168 prime numbers less than 1000. How many prime-looking numbers are there less than 1000?

Solution

  
  2020-07-09 06:38:46

Question 19

A faulty car odometer proceeds from digit 3 to digit 5, always skipping the digit 4, regardless of position. If the odometer now reads 002005, how many miles has the car actually traveled?

Solution

  
  2020-07-09 06:38:46

Question 20

For each in , define

Let , and for each integer . For how many values of in is ?

Solution

  
  2020-07-09 06:38:46

Question 21

How many ordered triples of integers , with , , and , satisfy both and ?

Solution

  
  2020-07-09 06:38:46

Question 22

A rectangular box is inscribed in a sphere of radius . The surface area of is 384, and the sum of the lengths of its 12 edges is 112. What is ?

Solution

  
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Question 23

Two distinct numbers and are chosen randomly from the set . What is the probability that is an integer?

Solution

  
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Question 24

Let . For how many polynomials does there exist a polynomial of degree 3 such that ?

Solution

  
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Question 25

Let be the set of all points with coordinates , where and are each chosen from the set . How many equilateral triangles have all their vertices in ?

Solution

  
  2020-07-09 06:38:46

Answer Keys


Question 1: D
Question 2: B
Question 3: B
Question 4: A
Question 5: B
Question 6: B
Question 7: C
Question 8: D
Question 9: A
Question 10: B
Question 11: E
Question 12: D
Question 13: D
Question 14: D
Question 15: C
Question 16: D
Question 17: A
Question 18: A
Question 19: B
Question 20: E
Question 21: C
Question 22: B
Question 23: B
Question 24: B
Question 25: C