2011 AMC 10A Problems

Problem 1

A cell phone plan costs each month, plus ¢ per text message sent, plus 10¢ for each minute used over hours. In January Michelle sent text messages and talked for hours. How much did she have to pay?

Solution

Problem 2

A small bottle of shampoo can hold 35 milliliters of shampoo, whereas a large bottle can hold 500 milliliters of shampoo. Jasmine wants to buy the minimum number of small bottles necessary to completely fill a large bottle. How many bottles must she buy?

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Problem 3

Suppose [ ] denotes the average of and , and { } denotes the average of , , and . What is {{1 1 0} [0 1] 0}?

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Problem 4

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Problem 5

At an elementary school, the students in third grade, fourth grade, and fifth grade run an average of , , and minutes per day, respectively. There are twice as many third graders as fourth graders, and twice as many fourth graders as fifth graders. What is the average number of minutes run per day by these students?

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Problem 6

Set has 20 elements, and set has 15 elements. What is the smallest possible number of elements in , the union of and ?

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Problem 7

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Problem 8

Last summer 30% of the birds living on Town Lake were geese, 25% were swans, 10% were herons, and 35% were ducks. What percent of the birds that were not swans were geese?

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Problem 9

A rectangular region is bounded by the graphs of the equations and , where and are all positive numbers. Which of the following represents the area of this region?

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Problem 10

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Problem 11

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Problem 12

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Problem 13

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Problem 14

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Problem 15

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Problem 16

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Problem 17

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Problem 18

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Problem 19

In 1991 the population of a town was a perfect square. Ten years later, after an increase of 150 people, the population was 9 more than a perfect square. Now, in 2011, with an increase of another 150 people, the population is once again a perfect square. Which of the following is closest to the percent growth of the town's population during this twenty-year period?

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Problem 20

Two points on the circumference of a circle of radius r are selected independently and at random. From each point a chord of length r is drawn in a clockwise direction. What is the probability that the two chords intersect?

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Problem 21

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Problem 22

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Problem 23

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Problem 24

Two distinct regular tetrahedra have all their vertices among the vertices of the same unit cube. What is the volume of the region formed by the intersection of the tetrahedra?

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Problem 25

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