2013 AMC 10A 考试题目
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1.
A taxi ride costs plus per mile traveled. How much does a -mile taxi ride cost?
Answer: C
Solution:
The mileage charge is .
Adding the fixed charge gives .
Thus, C is the correct answer.
2.
Alice is making a batch of cookies and needs cups of sugar. Unfortunately, her measuring cup holds only cup of sugar. How many times must she fill that cup to get the correct amount of sugar?
Answer: B
Solution:
Alice needs cups of sugar.
Each full measuring cup gives cup, so the number of fillings is .
Thus, B is the correct answer.
3.
Square has side length Point is on and the area of is What is
Answer: E
Solution:
We have by the formula for the area of a triangle that This gives us Thus, E is the correct answer.
4.
A softball team played ten games, scoring and runs. They lost by one run in exactly five games. In each of their other games, they scored twice as many runs as their opponent. How many total runs did their opponents score?
Answer: C
Solution:
Note that if they scored twice as many runs as their opponents, then they scored an even number of runs.
This means in the games where they scored and runs, their opponents scored and runs respectively.
This sums to
In the other games, their opponents scored and runs.
This sums to
The total number of runs is then Thus, C is the correct answer.
5.
Tom, Dorothy, and Sammy went on a vacation and agreed to split the costs evenly. During their trip Tom paid Dorothy paid and Sammy paid In order to share costs equally, Tom gave Sammy dollars, and Dorothy gave Sammy dollars. What is
Answer: B
Solution:
The total cost was , so each person's share was .
Tom paid less than his share, and Dorothy paid less than her share, so and .
Therefore .
Thus, B is the correct answer.
6.
Joey and his five brothers are ages and One afternoon two of his brothers whose ages sum to went to the movies, two brothers younger than went to play baseball, and Joey and the -year-old stayed home. How old is Joey?
Answer: D
Solution:
The age pairs that sum to are , , and .
The -year-old stayed home, so the movie pair cannot be . If and went to the movies, then the only remaining brother younger than would be the -year-old, not enough for baseball.
Thus the movie pair was , the baseball pair was , and Joey is the remaining brother, age .
Thus, D is the correct answer.
7.
A student must choose a program of four courses from a menu of courses consisting of English, Algebra, Geometry, History, Art, and Latin. This program must contain English and at least one mathematics course. In how many ways can this program be chosen?
Answer: C
Solution:
English is required, so choose the other courses from the courses Algebra, Geometry, History, Art, and Latin.
There are such choices, but one of them, History-Art-Latin, contains no mathematics course.
Therefore the number of valid programs is .
Thus, C is the correct answer.
8.
What is the value of
Answer: C
Solution:
Factoring out a we get:
Thus, C is the correct answer.
9.
In a recent basketball game, Shenille attempted only three-point shots and two-point shots. She was successful on of her three-point shots and of her two-point shots. Shenille attempted shots. How many points did she score?
Answer: B
Solution:
Let be the number of two-point shots and be the number of three-point shots.
Then, Shenille scores two-points shots and three-point shots, for a total score of
We know that
Thus, B is the correct answer.
10.
A flower bouquet contains pink roses, red roses, pink carnations, and red carnations. One third of the pink flowers are roses, three fourths of the red flowers are carnations, and six tenths of the flowers are pink. What percent of the flowers are carnations?
Answer: E
Solution:
Let the total number of flowers be There are pink flowers and red flowers.
Then there are pink roses, which means there are pink carnations.
There are also red carnations. This means there are carnations. This is of the total flowers.
Thus, E is the correct answer.
11.
A student council must select a two-person welcoming committee and a three-person planning committee from among its members. There are exactly ways to select a two-person team for the welcoming committee. It is possible for students to serve on both committees. In how many different ways can a three-person planning committee be selected?
Answer: A
Solution:
Let be the number of students. Then the number of ways to pick a two-person committee is We know that this equals so Factoring yields since there cannot be a negative number of students.
Then, the number of ways to pick a -person committee is
Thus, A is the correct answer.
12.
In and Points and are on sides and respectively, such that and are parallel to and respectively. What is the perimeter of parallelogram
Answer: C
Solution:
Note that and due to the parallel lines.
This tells us that and We have that the perimeter of is
Thus, C is the correct answer.
13.
How many three-digit numbers are not divisible by have digits that sum to less than and have the first digit equal to the third digit?
Answer: B
Solution:
Note that for the number to not be divisible by the units digits cannot be either or
Let be the hundreds and units digit and be the tens digit. Then we want Casing on the options of we get:
If is or then can be anything since
If then which gives us solutions.
If then which gives us solutions.
If then which gives us solutions.
If then which gives us solutions.
This gives us a total of solutions.
Thus, B is the correct solution.
14.
A solid cube of side length is removed from each corner of a solid cube of side length How many edges does the remaining solid have?
Answer: D
Solution:
Removing the cubes does not remove any edges from the original cube. It only adds edges.
After removing each cube, we can see that extra edges are added to the solid.
cubes are removed, which means edges are added to the original edges, for a total of edges.
Thus, D is the correct answer.
15.
Two sides of a triangle have lengths and The length of the altitude to the third side is the average of the lengths of the altitudes to the two given sides. How long is the third side?
Answer: D
Solution:
Let be the length of the altitude to the side of length and similarly define for the other given side.
We have that
The third altitude is the average of the other two, which makes its length
Let the third side have length Then
Thus, D is the correct answer.
16.
A triangle with vertices and is reflected about the line to create a second triangle. What is the area of the union of the two triangles?
Answer: E
Solution:
The reflected triangle has vertices , , and .
The line through and is , so it meets at . By symmetry, the union is two congruent triangles with vertical base from to .
That base has length , and each triangle has horizontal height . Hence the union area is .
Thus, E is the correct answer.
17.
Daphne is visited periodically by her three best friends: Alice, Beatrix, and Claire. Alice visits every third day, Beatrix visits every fourth day, and Claire visits every fifth day.
All three friends visited Daphne yesterday. How many days of the next -day period will exactly two friends visit her?
Answer: B
Solution:
Pairwise visits occur every , , and days.
In the next days, these pair counts are , , and .
All three visit every days, which happens times. Subtracting those days from each pair count gives .
Thus, B is the correct answer.
18.
Let points Quadrilateral is cut into equal area pieces by a line passing through This line intersects at point where these fractions are in lowest terms. What is
Answer: B
Solution:
Let the cutting line meet at . Drop perpendiculars from , , and to the -axis as in the diagram.
The areas of , trapezoid , and are , , and , respectively, so .
Thus has area . Since , the height of is .
The line has equation , so , giving . Therefore .
Thus, B is the correct answer.
19.
In base the number ends in the digit In base on the other hand, the same number is written as and ends in the digit For how many positive integers does the base--representation of end in the digit
Answer: C
Solution:
Note that the units digit of represents the remainder when the number is divided by the base.
The question then boils down to finding all numbers, such that leaves a remainder of when divided by
This means that must divide Also note that since otherwise the remainder cannot be
The prime factorization of is Then, has factors. It has factors less than namely and This means there are valid values for
Thus, C is the correct answer.
20.
A unit square is rotated about its center. What is the area of the region swept out by the interior of the square?
Answer: C
Solution:
Consider one quarter of the swept region and multiply its area by .
The sector has angle and radius , so its area is .
The two right-triangle pieces in that quarter have areas and .
Multiplying the quarter-area sum by gives .
Thus, C is the correct answer.
21.
A group of pirates agree to divide a treasure chest of gold coins among themselves as follows. The pirate to take a share takes of the coins that remain in the chest. The number of coins initially in the chest is the smallest number for which this arrangement will allow each pirate to receive a positive whole number of coins. How many coins does the pirate receive?
Answer: D
Solution:
Work backward. If coins remain for the th pirate, then before pirate took a share, the chest had times as many coins as it had afterward.
Therefore the initial number of coins is .
Since , the smallest that makes the initial number an integer is .
Thus, the th pirate receives coins, and D is the correct answer.
22.
Six spheres of radius are positioned so that their centers are at the vertices of a regular hexagon of side length The six spheres are internally tangent to a larger sphere whose center is the center of the hexagon. An eighth sphere is externally tangent to the six smaller spheres and internally tangent to the larger sphere. What is the radius of this eighth sphere?
Answer: B
Solution:
The centers of the six radius- spheres form a regular hexagon of side length , so each is units from the large sphere's center. Hence the large sphere has radius .
Let the eighth sphere have radius , and let its center be distance from the large sphere's center. Internal tangency gives , so .
Using the right triangle between the large center, a small-sphere center, and the eighth-sphere center, . Thus , so .
Thus, B is the correct answer.
23.
In and A circle with center and radius intersects at points and Moreover and have integer lengths. What is
Answer: D
Solution:
By power of a point from , .
This equals .
Both and are integers, so is an integer factor paired with . Also , so the only possible pair is , .
Thus, D is the correct answer.
24.
Central High School is competing against Northern High School in a backgammon match. Each school has three players, and the contest rules require that each player play two games against each of the other school's players. The match takes place in six rounds, with three games played simultaneously in each round. In how many different ways can the match be scheduled?
Answer: E
Solution:
Label Central's players and Northern's players .
Player 's six-round opponent string contains two each of , so it can be chosen in ways.
For a fixed -string, say , player 's string must also contain two each of and cannot match 's opponent in any position.
If 's first two entries are in either order, then the middle two entries must be in either order and the last two must be in either order, giving strings. The two remaining possibilities are and , for total -strings.
Once and are scheduled, 's schedule is forced. Hence there are schedules.
Thus, E is the correct answer.
25.
All diagonals are drawn in a regular octagon. At how many distinct points in the interior of the octagon (not on the boundary) do two or more diagonals intersect?
Answer: A
Solution:
If no three diagonals were concurrent, each choice of vertices would determine one interior intersection, giving .
The long diagonals through opposite vertices all meet at the center, so the center was counted times and should be counted once. Subtract .
There are also symmetric points where diagonals meet. Each was counted times and should be counted once, so subtract .
The number of distinct interior intersection points is .
Thus, A is the correct answer.