## 2019AMC10B真题及答案解析

首发文字版，2019amc10b晋级2019 AIME cutoff 分数线待公布

参考答案见文末（仅供参考）

## Problem 1

Alicia had two containers. The first was full of water and the second was empty. She poured all the water from the first container into the second container, at which point the second container was full of water. What is the ratio of the volume of the first container to the volume of the second container?

## Problem 2

Consider the statement, "If is not prime, then is prime." Which of the following values of is a counterexample to this statement.

## Problem 3

In a high school with students, of the seniors play a musical instrument, while of the non-seniors do not play a musical instrument. In all, of the students do not play a musical instrument. How many non-seniors play a musical instrument?

## Problem 4

All lines with equation such that form an arithmetic progression pass through a common point. What are the coordinates of that point?

## Problem 5

Triangle lies in the first quadrant. Points , , and are reflected across the line to points , , and ,respectively. Assume that none of the vertices of the triangle lie on the line . Which of the following statements is __ not__always true?

Triangle lies in the first quadrant.

Triangles and have the same area.

The slope of line is .

The slopes of lines and are the same.

Lines and are perpendicular to each other.

## Problem 6

There is a real such that . What is the sum of the digits of ?

## Problem 7

Each piece of candy in a store costs a whole number of cents. Casper has exactly enough money to buy either 12 pieces of red candy, 14 pieces of green candy, 15 pieces of blue candy, or pieces of purple candy. A piece of purple candy costs 20 cents. What is the smallest possible value of ?

## Problem 8

The figure below shows a square and four equilateral triangles, with each triangle having a side lying on a side of the square, such that each triangle has side length 2 and the third vertices of the triangles meet at the center of the square. The region inside the square but outside the triangles is shaded. What is the area of the shaded region?

[Asymptote diagram needed]

Problem 9

The function is defined byfor all real numbers , where denotes the greatest integer less than or equal to the real number . What is the range of ?

## Problem 10

In a given plane, points and are units apart. How many points are there in the plane such that the perimeter of is units and the area of is square units?

## Problem 11

Two jars each contain the same number of marbles, and every marble is either blue or green. In Jar 1 the ratio of blue to green marbles is 9:1, and the ratio of blue to green marbles in Jar 2 is 8:1. There are 95 green marbles in all. How many more blue marbles are in Jar 1 than in Jar 2?

5 10 25 45 50

## Problem 12

What is the greatest possible sum of the digits in the base-seven representation of a positive integer less than ?

## Problem 13

What is the sum of all real numbers for which the median of the numbers and is equal to the mean of those five numbers?

## Problem 14

The base-ten representation for is , where , , and denote digits that are not given. What is ?

## Problem 15

Two right triangles, and , have areas of 1 and 2, respectively. One side length of one triangle is congruent to a different side length in the other, and another side length of the first triangle is congruent to yet another side length in the other. What is the product of the third side lengths of and ?

**A) 28/3 B) 10 C) 32/3 D)34/3 E) 12**

## Problem 16

In with a right angle at point lies in the interior of and point lies in the interior of so that and the ratio What is the ratio

## Problem 17

A red ball and a green ball are randomly and independently tossed into bins numbered with positive integers so that for each ball, the probability that it is tossed into bin is for What is the probability that the red ball is tossed into a higher-numbered bin than the green ball?

## Problem 18

Henry decides one morning to do a workout, and he walks of the way from his home to his gym. The gym is kilometers away from Henry's home. At that point, he changes his mind and walks of the way from where he is back toward home. When he reaches that point, he changes his mind again and walks of the distance from there back toward the gym. If Henry keeps changing his mind when he has walked of the distance toward either the gym or home from the point where he last changed his mind, he will get very close to walking back and forth between a point kilometers from home and a point kilometers from home. What is ?

## Problem 19

Let be the set of all positive integer divisors of How many numbers are the product of two distinct elements of

## Problem 20

As shown in the figure, line segment is trisected by points and so that Three semicircles of radius and have their diameters on and are tangent to line at and respectively. A circle of radius has its center on The area of the region inside the circle but outside the three semicircles, shaded in the figure, can be expressed in the formwhere and are positive integers and and are relatively prime. What is ?

## Problem 21

Debra flips a fair coin repeatedly, keeping track of how many heads and how many tails she has seen in total, until she gets either two heads in a row or two tails in a row, at which point she stops flipping. What is the probability that she gets two heads in a row but she sees a second tail before she sees a second head?

## Problem 22

Raashan, Sylvia, and Ted play the following game. Each starts with . A bell rings every seconds, at which time each of the players who currently have money simultaneously chooses one of the other two players independently and at random and gives to that player. What is the probability that after the bell has rung times, each player will have ? (For example, Raashan and Ted may each decide to give to Sylvia, and Sylvia may decide to give her her dollar to Ted, at which point Raashan will have , Sylvia will have , and Ted will have , and that is the end of the first round of play. In the second round Rashaan has no money to give, but Sylvia and Ted might choose each other to give their to, and the holdings will be the same at the end of the second round.)

## Problem 23

Points and lie on circle in the plane. Suppose that the tangent lines to at and intersect at a point on the -axis. What is the area of ?

## Problem 24

Define a sequence recursively by andfor all nonnegative integers Let be the least positive integer such thatIn which of the following intervals does lie?

## Problem 25

How many sequences of s and s of length are there that begin with a , end with a , contain no two consecutive s, and contain no three consecutive s?

## AMC8/AMC10/AMC12/AIME

## 报名及辅导请联系

Aaron 李老师 15618605663 微信：linstitute4