2002 AMC 8 考试答案
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All of the real AMC 8 and AMC 10 problems in our complete solution collection are used with official permission of the Mathematical Association of America (MAA).
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1.
A circle and two distinct lines are drawn on a sheet of paper. What is the largest possible number of points of intersection of these figures?
Solution:
A line and a circle can intersect at no more than two points, and two distinct lines can intersect at no more than one point.
Arrange the two lines so each meets the circle twice and the two lines meet at a different point. This gives
Thus, D is the correct answer.
2.
How many different combinations of bills and bills can be used to make a total of ? Order does not matter in this problem.
Solution:
Since the total is odd, the number of bills must be odd.
One bill leaves , which is six bills. Three bills leave , which is one bill. Five bills is too much.
Therefore, there are combinations.
Thus, A is the correct answer.
3.
What is the smallest possible average of four distinct positive even integers?
Solution:
To get the smallest possible average, we want to use the smallest positive even integers.
This can be achieved as follows:
Thus, C is the correct answer.
4.
The year is a palindrome (a number that reads the same from left to right as it does from right to left). What is the product of the digits of the next year after that is a palindrome?
Solution:
We don't want to increase the thousands digit, so we can keep that as
This means that we have to increase the tens and hundreds digits to to yield the next palindrome of The product of its digits is
Thus, B is the correct answer.
5.
Carlos Montado was born on Saturday, November On what day of the week will Carlos be days old?
Monday
Wednesday
Friday
Saturday
Sunday
Solution:
The days of the week cycle every days. After days, the day of the week will still be Saturday.
After more days, the day of the week will be Friday.
Thus, C is the correct answer.
6.
A birdbath is designed to overflow so that it will be self-cleaning. Water flows in at the rate of milliliters per minute and drains at the rate of milliliters per minute. One of these graphs shows the volume of water in the birdbath during the filling time and continuing into the overflow time. Which one is it?
Solution:
Before the birdbath overflows, it gains milliliters of water per minute, so its volume increases steadily.
Once the birdbath is full, the incoming extra water overflows, so the volume remains constant. Only graph A shows an increasing line followed by a horizontal line.
Thus, A is the correct answer.
7.
The students in Mrs. Sawyer's class were asked to do a taste test of five kinds of candy. Each student chose one kind of candy. A bar graph of their preferences is shown. What percent of her class chose candy
Solution:
There are a total of students in the class. The percent that chose is
Thus, E is the correct answer.
8.
Problems and use the data found in the accompanying paragraph and table.
Juan’s Old Stamping Grounds
Juan organizes the stamps in his collection by country and by the decade in which they were issued. The prices he paid for them at a stamp shop were: Brazil and France, ¢ each, Peru ¢ each, and Spain ¢ each. (Brazil and Peru are South American countries and France and Spain are in Europe.)
Number of Stamps by Decade
How many of his European stamps were issued in the ‘s?
Solution:
Note that France and Spain are the European countries. The number of ‘s stamps from these countries respectively is and for a total of stamps.
Thus, D is the correct answer.
9.
His South American stamps issued before the ‘s cost him
Solution:
Brazil and Peru are the South American countries.
Brazil has stamps before the ‘s, costing cents. Peru has such stamps, costing cents.
The total cost is cents, or .
Thus, B is the correct answer.
10.
The average price of his ‘s stamps is closest to
¢
¢
¢
¢
¢
Solution:
The ‘s stamps cost cents.
There are stamps, so the average cost is , a little more than cents and closest to cents.
Thus, E is the correct answer.
11.
A sequence of squares is made of identical square tiles. The edge of each square is one tile length longer than the edge of the previous square. The first three squares are shown. How many more tiles does the seventh square require than the sixth?
Solution:
The sixth and seventh squares have side lengths and tile lengths.
They use and tiles, respectively, so the seventh square requires more tiles.
Thus, C is the correct answer.
12.
A board game spinner is divided into three regions labeled and The probability of the arrow stopping on region is and on region is The probability of the arrow stopping on region is
Solution:
The total probability is We need to subtract the probability of the spinner landing on and to get which is
Thus, B is the correct answer.
13.
For his birthday, Bert gets a box that holds jellybeans when filled to capacity. A few weeks later, Carrie gets a larger box full of jellybeans. Her box is twice as high, twice as wide and twice as long as Bert's. Approximately, how many jellybeans did Carrie get?
Solution:
The larger box will have approximately jellybeans.
Thus, E is the correct answer.
14.
A merchant offers a large group of items at off. Later, the merchant takes off these sale prices and claims that the final price of these items is off the original price. The total discount is
Solution:
Let the original price be . After the discount, the price is .
Taking another off that sale price leaves .
The customer pays of the original price, so the total discount is .
Thus, B is the correct answer.
15.
Which of the following polygons has the largest area?
Solution:
The number of boxes enclosed by each polygon can be obtained by dividing the polygon into unit squares and right triangles with sidelength and adding up their values.
The unit squares count as and the triangles count as
has a total area of has has has and has
Thus, E is the correct answer.
16.
Right isosceles triangles are constructed on the sides of a right triangle, as shown. A capital letter represents the area of each triangle. Which one of the following is true?
Solution:
For a right isosceles triangle built on a side of length , the two legs have length , so its area is .
These values satisfy , and the other listed equations do not.
Thus, E is the correct answer.
17.
In a mathematics contest with ten problems, a student gains points for a correct answer and loses points for an incorrect answer. If Olivia answered every problem and her score was how many correct answers did she have?
Solution:
Let be the number of correct answers. Then she answered questions incorrectly.
This gives her a total score of
We know that this equals and solving yields
Thus, C is the correct answer.
18.
Gage skated hr min each day for days and hr min each day for days. How long would he have to skate the ninth day in order to average minutes of skating each day for the entire time?
hr
hr min
hr min
hr min
hr
Solution:
Gage has skated a total of
For an average of minutes over days, Gage must have skated a total of
This means that Gage must skate on the last day. Note that minutes is the same as hours.
Thus, E is the correct answer.
19.
How many whole numbers between and contain exactly one
Solution:
Note that the digit can either be the tens or the units digit. This gives us options for this.
There are options for each of the other digits for a total of numbers.
Thus, D is the correct answer.
20.
The area of triangle is square inches. Points and are midpoints of congruent segments and Altitude bisects The area (in square inches) of the shaded region is
Solution:
Since and bisects , altitude splits into two congruent triangles. The left half has area .
In , point is the midpoint of . The horizontal segment through meets halfway up, so the small top triangle is similar to with scale factor . Its area is therefore of , or .
The shaded region is the rest of the left half, so its area is .
Thus, D is the correct answer.
21.
Harold tosses a nickel four times. The probability that he gets at least as many heads as tails is
Solution:
There are equally likely outcomes for four coin tosses.
At least as many heads as tails means getting , , or heads. The number of such outcomes is
Thus the probability is .
Thus, E is the correct answer.
22.
Six cubes, each an inch on an edge, are fastened together, as shown. Find the total surface area in square inches. Include the top, bottom, and sides.
Solution:
We can count the number of unexposed sides to find how many sides contribute to the surface area.
Three cubes have side unexposed, two cubes have sides unexposed, and one cube has sides unexposed.
This gives us a total of unexposed sides, which gives us exposed sides.
Each exposed side contributes to the surface area, for a total surface area of
Thus, C is the correct answer.
23.
A corner of a tiled floor is shown. If the entire floor is tiled in this way and each of the four corners looks like this one, then what fraction of the tiled floor is made of darker tiles?
Solution:
Notice that there are repeating regions with the same pattern (they might be rotated differently).
In this region, there are three unit squares, and two triangles that combine to form another unit square.
This makes the area of the darker region and the whole region The desired fraction is then
Thus, B is the correct answer.
24.
Miki has a dozen oranges of the same size and a dozen pears of the same size. Miki uses her juicer to extract ounces of pear juice from pears and ounces of orange juice from oranges. She makes a pear-orange juice blend from an equal number of pears and oranges. What percent of the blend is pear juice?
Solution:
Use pears and oranges, which is an equal number of each fruit.
Since pears make ounces, pears make ounces. Since oranges make ounces, oranges make ounces.
The blend has ounces total, of which ounces is pear juice. The pear-juice percent is .
Thus, B is the correct answer.
25.
Loki, Moe, Nick and Ott are good friends. Ott had no money, but the others did. Moe gave Ott one-fifth of his money, Loki gave Ott one-fourth of his money and Nick gave Ott one-third of his money. Each gave Ott the same amount of money. What fractional part of the group's money does Ott now have?
Solution:
WLOG, assume that everyone gave Ott This means that Moe had Loki had and Nick had originally.
Ott now has and the total amount of money is
This means that Ott has of the group's money.
Thus, B is the correct answer.