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AMC 12 2016 B

Question 1

What is the value of when ?

Solution

  
  2020-07-09 06:38:19

Question 2

The harmonic mean of two numbers can be calculated as twice their product divided by their sum. The harmonic mean of and is closest to which integer?

Solution

  
  2020-07-09 06:38:19

Question 3

Let . What is the value of ?

Solution

  
  2020-07-09 06:38:19

Question 4

The ratio of the measures of two acute angles is , and the complement of one of these two angles is twice as large as the complement of the other. What is the sum of the degree measures of the two angles?

Solution

  
  2020-07-09 06:38:19

Question 5

The War of started with a declaration of war on Thursday, June , . The peace treaty to end the war was signed days later, on December , . On what day of the week was the treaty signed?

Solution

  
  2020-07-09 06:38:19

Question 6

All three vertices of lie on the parabola defined by , with at the origin and parallel to the -axis. The area of the triangle is . What is the length of ?

Solution

  
  2020-07-09 06:38:19

Question 7

Josh writes the numbers . He marks out , skips the next number , marks out , and continues skipping and marking out the next number to the end of the list. Then he goes back to the start of his list, marks out the first remaining number , skips the next number , marks out , skips , marks out , and so on to the end. Josh continues in this manner until only one number remains. What is that number?

Solution

  
  2020-07-09 06:38:19

Question 8

A thin piece of wood of uniform density in the shape of an equilateral triangle with side length inches weighs ounces. A second piece of the same type of wood, with the same thickness, also in the shape of an equilateral triangle, has side length of inches. Which of the following is closest to the weight, in ounces, of the second piece?

Solution

  
  2020-07-09 06:38:19

Question 9

Carl decided to fence in his rectangular garden. He bought fence posts, placed one on each of the four corners, and spaced out the rest evenly along the edges of the garden, leaving exactly yards between neighboring posts. The longer side of his garden, including the corners, has twice as many posts as the shorter side, including the corners. What is the area, in square yards, of Carl???s garden?

Solution

  
  2020-07-09 06:38:19

Question 10

A quadrilateral has vertices , , , and , where and are integers with . The area of is . What is ?

Solution

  
  2020-07-09 06:38:19

Question 11

How many squares whose sides are parallel to the axes and whose vertices have coordinates that are integers lie entirely within the region bounded by the line , the line and the line

Solution 1

Let (X0, Y0) be the lower left vertex of square, and (X1, Y1) be the upper right vertex of square.

Let's consider 4 cases:

1. Side of square = 1

When X0 = 1, we can move Y0 to 0-2 without making Y1 1-3 go above pi * X0 = 3.14 (3 possibilities)
When X0 = 2, we can move Y0 to 0-5 without making Y1 2-6 go above pi * X0 = 6.28 (6 possibilities)
When X0 = 3, we can move Y0 to 0-8 without making Y1 1-9 go above pi * X0 = 9.42 (9 possibilities)
When X0 = 4, we can move Y0 to 0-11 without making Y1 1-12 go above pi * X0 = 12.56 (12 possibilities)

2. Side of square = 2

When X0 = 1, we can move Y0 to 0,1 without making Y1 2,3 go above pi * X0 = 3.14 (2 possibilities)
When X0 = 2, we can move Y0 to 0,1,2,3,4 without making Y1 2,3,4,5,6 go above pi * X0 = 6.28 (5 possibilities)
When X0 = 3, we can move Y0 to 0-7 without making Y1 2-9 go above pi * X0 = 9.42 (8 possibilities)
When X0 = 4, X1=6, so out of range horizontally

3. Side of square = 3

When X0 = 1, we can move Y0 to 0 without making Y1 3 go above pi * X0 = 3.14 (1 possibilities)
When X0 = 2, we can move Y0 to 0,1,2,3 without making Y1 3,4,5,6 go above pi * X0 = 6.28 (4 possibilities)
When X0 = 3, X1=6, so out of range horizontally

4. Side of square = 4

Out of range horizontally or vertically no matter how you place the square.
  
jimmy  2016-09-30 20:07:20

Solution 2

I am posting this diagram so it will be easier for you to visualize the solution.
  
jimmy  2016-09-23 17:07:02

Question 12

All the numbers are written in a array of squares, one number in each square, in such a way that if two numbers are consecutive then they occupy squares that share an edge. The numbers in the four corners add up to . What is the number in the center?

Solution

  
  2020-07-09 06:38:20

Question 13

Alice and Bob live miles apart. One day Alice looks due north from her house and sees an airplane. At the same time Bob looks due west from his house and sees the same airplane. The angle of elevation of the airplane is from Alice's position and from Bob's position. Which of the following is closest to the airplane's altitude, in miles?

Solution

  
  2020-07-09 06:38:20

Question 14

The sum of an infinite geometric series is a positive number , and the second term in the series is . What is the smallest possible value of

Solution

  
  2020-07-09 06:38:20

Question 15

All the numbers are assigned to the six faces of a cube, one number to each face. For each of the eight vertices of the cube, a product of three numbers is computed, where the three numbers are the numbers assigned to the three faces that include that vertex. What is the greatest possible value of the sum of these eight products?

Solution

  
  2020-07-09 06:38:20

Question 16

In how many ways can be written as the sum of an increasing sequence of two or more consecutive positive integers?

Solution

  
  2020-07-09 06:38:20

Question 17

In shown in the figure, , , , and is an altitude. Points and lie on sides and , respectively, so that and are angle bisectors, intersecting at and , respectively. What is ?

Solution

First you need to know Herons' formula which calculates area of a triangle given its 3 sides.
https://www.homesweetlearning.com/resources/math/math910/geometry/areas.html

From Herons' formula, we will know the area of triangle ABC is 12 * square root of 5.
Then we will know Height AH = 3 * square root of 5
Then applying Pythagorean Theorem to triangle ABH, we will know BH=2, then we will know CH=6
Apply angle bisector theorem on triangle ACH, we get AP:PH = 9:6
Apply angle bisector theorem on triangle ABH, we get AQ:QH = 7:2.

Now you can figure out PQ:

PH = QH+PQ
AQ = AP+PQ

AP/(QH+PQ) = 9/6
(AP+PQ)/QH = 7/2
AP+PQ+QH=3 * square root of 5
  
jimmy  2016-10-01 21:51:14

Question 18

What is the area of the region enclosed by the graph of the equation

Solution

  
  2020-07-09 06:38:20

Question 19

Tom, Dick, and Harry are playing a game. Starting at the same time, each of them flips a fair coin repeatedly until he gets his first head, at which point he stops. What is the probability that all three flip their coins the same number of times?

Solution

  
  2020-07-09 06:38:20

Question 20

A set of teams held a round-robin tournament in which every team played every other team exactly once. Every team won games and lost games; there were no ties. How many sets of three teams were there in which beat , beat , and beat

Solution

  
  2020-07-09 06:38:20

Question 21

Let be a unit square. Let be the midpoint of . For let be the intersection of and , and let be the foot of the perpendicular from to . What is

Solution

  
  2020-07-09 06:38:20

Question 22

For a certain positive integer less than , the decimal equivalent of is , a repeating decimal of period of , and the decimal equivalent of is , a repeating decimal of period . In which interval does lie?

Solution

  
  2020-07-09 06:38:20

Question 23

What is the volume of the region in three-dimensional space defined by the inequalities and ?

Solution

  
  2020-07-09 06:38:20

Question 24

There are exactly ordered quadruplets such that and . What is the smallest possible value for ?

Solution

  
  2020-07-09 06:38:20

Question 25

The sequence is defined recursively by , , and for . What is the smallest positive integer such that the product is an integer?

Solution

  
  2020-07-09 06:38:20

Answer Keys


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