ΒΆ 2019 AMC 10B Problems and Solutions
Problem Set Workbook
Access the downloadable workbook for 2019 AMC 10B problems here.
Discussion Forum
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Individual Problems and Solutions
For problems and detailed solutions to each of the 2019 AMC 10B problems, please refer below:
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 smaller container to the volume of the larger container?
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Problem 2: Consider the statement, "If is not prime, then is prime." Which of the following values of is a counterexample to this statement?
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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?
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Problem 4: All lines with equation such that form an arithmetic progression pass through a common point. What are the coordinates of that point?
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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 always true?
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A. Triangle lies in the first quadrant.
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Problem 6: A positive integer satisfies the equation . What is the sum of the digits of ?
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Problem 7: Each piece of candy in a shop costs a whole number of cents. Casper has exactly enough money to buy either pieces of red candy, pieces of green candy, pieces of blue candy, or pieces of purple candy. A piece of purple candy costs cents. What is the least possible value of ?
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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 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?
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Problem 9: The function is defined by
for all real numbers , where denotes the greatest integer less than or equal to the real number . What is the range of ?
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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?
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Problem 11: Two jars each contain the same number of marbles, and every marble is either blue or green. In Jar the ratio of blue to green marbles is , and the ratio of blue to green marbles in Jar is . There are green marbles in all. How many more blue marbles are in Jar than in Jar ?
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Problem 12: What is the greatest possible sum of the digits in the base-seven representation of a positive integer less than ?
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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?
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Problem 14: The base-ten representation for is , where , and denote digits that are not given. What is ?
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Problem 15: Right triangles and have areas and , respectively. A side of is congruent to a side of , and a different side of is congruent to a different side of . What is the square of the product of the lengths of the other (third) sides of and ?
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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 ?
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Problem 17: A red ball and a green ball are randomly and independently tossed into bins numbered with the 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?
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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 ?
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Problem 19: Let be the set of all positive integer divisors of . How many numbers are the product of two distinct elements of ?
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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 , lie in the same halfplane determined by line , and are tangent to line at , , and , respectively. A circle of radius has its center at . The area of the region inside the circle but outside the three semicircles, shaded in the figure, can be expressed in the form
where , and are positive integers and and are relatively prime. What is ?
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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?
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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 has 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 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 Raashan 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.)
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Problem 23: Points and lie on a circle in the plane. Suppose that the tangent lines to at and intersect at a point on the -axis. What is the area of ?
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Problem 24: Define a sequence recursively by and
for all nonnegative integers . Let be the least positive integer such that
In which of the following intervals does lie?
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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?
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The problems on this page are the property of the MAA's American Mathematics Competitions