2001 AMC 8 Solutions
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All problems are used with official legal permission of the Mathematical Association of America (MAA).
1.
Casey’s shop class is making a golf trophy. He has to paint dimples on a golf ball. If it takes him seconds to paint one dimple, how many minutes will he need to do his job?
Small Hint:
Convert the total painting time to seconds first
Big Hint:
There are seconds in one minute
Solution:
It will take Casey seconds to do the job. Since seconds make one minute, this is minutes.
Thus, D is the correct answer.
2.
I’m thinking of two whole numbers. Their product is and their sum is What is the larger number?
Small Hint:
List the factor pairs of
Big Hint:
Find the pair whose sum is
Solution:
The factor pairs of are and .
The only pair with sum is , so the larger number is .
Thus, D is the correct answer.
3.
Granny Smith has Elberta has more than Anjou and Anjou has one-third as much as Granny Smith. How many dollars does Elberta have?
Small Hint:
Find one-third of Granny Smith’s money
Big Hint:
Elberta has more than Anjou
Solution:
Anjou has . Elberta has more than Anjou, so Elberta has .
Thus, E is the correct answer.
4.
The digits and are each used once to form the smallest possible even five-digit number. The digit in the tens place is
Small Hint:
The number must end in or
Big Hint:
Make the earlier digits as small as possible
Solution:
The units digit must be or . If it is , arranging the remaining digits as small as possible gives . If it is , the smallest arrangement is , which is smaller. Therefore the smallest even number is , whose tens digit is .
Thus, E is the correct answer.
5.
On a dark and stormy night Snoopy suddenly saw a flash of lightning. Ten seconds later he heard the sound of thunder. The speed of sound is feet per second and one mile is feet. Estimate, to the nearest half-mile, how far Snoopy was from the flash of lightning.
Small Hint:
Use distance equals rate times time
Big Hint:
Compare the distance with miles
Solution:
In seconds, the thunder was able to travel feet.
Note that miles is about feet, which is close to what we found above.
Thus, C is the correct answer.
6.
Six trees are equally spaced along one side of a straight road. The distance from the first tree to the fourth is feet. What is the distance in feet between the first and last trees?
Small Hint:
The first to fourth trees contain three equal gaps
Big Hint:
The first to last trees contain five equal gaps
Solution:
There are gaps between the first and fourth trees, which means that one gap is feet long.
There are gaps between the first and last trees. This means that they are feet apart.
Thus, B is the correct answer.
7.
Problems and are about these kites.
To promote her school’s annual Kite Olympics, Genevieve makes a small kite and a large kite for a bulletin board display. The kites look like the one in the diagram. For her small kite Genevieve draws the kite on a one-inch grid. For the large kite she triples both the height and width of the entire grid.
What is the number of square inches in the area of the small kite?
Small Hint:
Use the kite diagonals on the grid
Big Hint:
The area is half the product of the diagonals
Solution:
Recall that the area of a kite is the product of its diagonals divided by
Therefore, the area of the small kite is
Thus, A is the correct answer.
8.
Genevieve puts bracing on her large kite in the form of a cross connecting opposite corners of the kite. How many inches of bracing material does she need?
Small Hint:
The bracing is the sum of the two diagonals
Big Hint:
Tripling the grid triples both diagonal lengths
Solution:
The long diagonal is units, and the short one is units.
In the large kite, one unit is inches, so the total amount of bracing material needed is
Thus, E is the correct answer.
9.
The large kite is covered with gold foil. The foil is cut from a rectangular piece that just covers the entire grid. How many square inches of waste material are cut off from the four corners?
Small Hint:
Tripling both dimensions multiplies area by
Big Hint:
The waste area equals the large kite area
Solution:
The area of the entire grid would be The area of the kite is one-half this area from the formula for the area of the kite, so the wasted material is
Thus, D is the correct answer.
10.
A collector offers to buy state quarters for of their face value. At that rate how much will Bryden get for his four state quarters?
Small Hint:
Four quarters have face value
Big Hint:
means times face value
Solution:
Four state quarters have face value .
Since , the collector pays times face value, or .
Thus, A is the correct answer.
11.
Points and have these coordinates: and What is the area of quadrilateral
Small Hint:
View as a trapezoid
Big Hint:
The parallel vertical sides have lengths and
Solution:
We can see that is a trapezoid since
Recall that the formula for the area of a trapezoid is
Plugging in and we get that
Thus, C is the correct answer.
12.
If then
Small Hint:
Evaluate first
Big Hint:
Then use the result as the first input with
Solution:
We can evaluate it as follows
Thus, A is the correct answer.
13.
Of the students in Richelle’s class, prefer chocolate pie, prefer apple, and prefer blueberry. Half of the remaining students prefer cherry pie and half prefer lemon. For Richelle’s pie graph showing this data, how many degrees should she use for cherry pie?
Small Hint:
Find how many students remain after the first three pies
Big Hint:
Cherry is half of the remaining group
Solution:
The number of students that prefer cherry or lemon pie is Half of these like cherry pie, which is
The number of degrees for cherry pie would then be
Thus, D is the correct answer.
14.
Tyler has entered a buffet line in which he chooses one kind of meat, two different vegetables and one dessert. If the order of food items is not important, how many different meals might he choose?
Meat: beef, chicken, pork
Vegetables: baked beans, corn, potatoes, tomatoes
Dessert: brownies, chocolate cake, chocolate pudding, ice cream
Small Hint:
Choose the two vegetables as an unordered pair
Big Hint:
Multiply meat choices, vegetable pairs, and dessert choices
Solution:
He has choices for the meat and choices for dessert.
He must choose of the vegetables. Since order does not matter, there are vegetable choices.
This gives possible meals.
Thus, C is the correct answer.
15.
Homer began peeling a pile of potatoes at the rate of potatoes per minute. Four minutes later Christen joined him and peeled at the rate of potatoes per minute. When they finished, how many potatoes had Christen peeled?
Small Hint:
Find how many potatoes remain when Christen starts
Big Hint:
After that, their combined rate is per minute
Solution:
Homer had peeled potatoes by the time Christen joined him, leaving potatoes.
Together, Homer and Christen peel potatoes per minute, taking them minutes to peel the rest.
In minutes, Christen peeled potatoes.
Thus, A is the correct answer.
16.
A square piece of paper, inches on a side, is folded in half vertically. Both layers are then cut in half parallel to the fold. Three new rectangles are formed, a large one and two small ones. What is the ratio of the perimeter of one of the small rectangles to the perimeter of the large rectangle?
Small Hint:
After folding, the paper is a rectangle
Big Hint:
The small rectangles are
Solution:
The square is folded in half to create a rectangle.
Cutting the folded paper in half parallel to the fold gives two small rectangles and one large rectangle.
The ratio of the perimeter of a small rectangle to the perimeter of the large rectangle is
Thus, E is the correct answer.
17.
For the game show Who Wants To Be a Millionaire? the dollar values of each question are shown in the following table (where ). Between which two questions is the percent increase of the value the smallest?
From to
From to
From to
From to
From to
Small Hint:
Most listed increases are doublings
Big Hint:
Compare the few increases that are not exactly
Solution:
Most of the listed increases are doublings, which are increases.
The exceptions among the answer choices are from to , from to , and from to .
These percent increases are , , and , which is about .
The smallest is from question to question .
Thus, B is the correct answer.
18.
Two dice are thrown. What is the probability that the product of the two numbers is a multiple of
Small Hint:
The product is a multiple of exactly when a die shows
Big Hint:
It is easier to count no die showing
Solution:
The only way for the product to be a multiple of is if at least one of the rolls is
We can do complementary counting. The probability that neither rolls is a is
Therefore, the probability that at least one roll is a is
Thus, D is the correct answer.
19.
Car traveled at a constant speed for a given time. This is shown by the dashed line. Car traveled at twice the speed for the same distance. If Car ’s speed and time are shown as a solid line, which graph illustrates this?
Small Hint:
Twice the speed means half the time for the same distance
Big Hint:
The solid line should be higher and shorter
Solution:
Car travels at twice the speed of car so it is represented by a point that is twice as high on the speed axis as car
Since car travels at the same distance as car but at a faster speed, it takes half the time to complete the trip.
Therefore, the line representing car ’s speed is half the length of the line representing car ’s speed.
Both lines are horizontal because the speeds are constant. Examining the given graphs, the only one that meets these conditions is graph D .
Thus, D is the correct answer.
20.
Kaleana shows her test score to Quay, Marty and Shana, but the others keep theirs hidden. Quay thinks, “At least two of us have the same score.” Marty thinks, “I didn’t get the lowest score.” Shana thinks, “I didn’t get the highest score.” List the scores from lowest to highest for Marty (), Quay () and Shana ().
Small Hint:
Quay only sees Kaleana’s score
Big Hint:
Use each hidden-score statement relative to Kaleana
Solution:
Since Quay only knows Kaleana’s score, we get that Quay and Kaleana have the same score, so
Marty knows that his score is higher than Kaleana’s, so Shana knows that her score is lower than Kaleana’s, so
Substituting for we get the following inequality:
Thus, A is the correct answer.
21.
The mean of a set of five different positive integers is The median is The maximum possible value of the largest of these five integers is
Small Hint:
The five numbers sum to
Big Hint:
Make the other four numbers as small as possible
Solution:
The median of the set of numbers is the third largest number, which is There are two numbers less than and two numbers greater than it.
The mean of the set is so the sum of all the numbers is In order to maximize the largest number with this sum, the other numbers must be as small as possible.
The two numbers less than must be positive and distinct, so they must be and
The number immediately after must also be as small as possible, so it must be
Therefore, the remaining number, the maximum possible value in the set, is
Thus, D is the correct answer.
22.
On a twenty-question test, each correct answer is worth points, each unanswered question is worth point and each incorrect answer is worth points. Which of the following scores is NOT possible?
Small Hint:
Check scores near
Big Hint:
With correct answers, only two scores are possible
Solution:
With correct answers, the score is .
With correct answers, the score is either or , depending on whether the remaining question is incorrect or unanswered.
With correct answers, the remaining two questions can contribute , , or points, giving , , or .
Thus the listed scores are possible, while is not.
Thus, E is the correct answer.
23.
Points and are vertices of an equilateral triangle, and points and are midpoints of its sides. How many noncongruent triangles can be drawn using any three of these six points as vertices?
Small Hint:
Classify triangles by side lengths
Big Hint:
Use symmetry to avoid recounting congruent cases
Solution:
Using the side length of the small equilateral triangles as one unit, the possible triangle side-length patterns are:
equilateral with sides ; equilateral with sides ; small isosceles with sides ; and larger isosceles with sides .
These four patterns all occur in the figure, and symmetry shows every triangle formed by three of the six points matches one of them.
Thus there are noncongruent triangles.
Thus, D is the correct answer.
24.
Each half of this figure is composed of red triangles, blue triangles and white triangles. When the upper half is folded down over the centerline, pairs of red triangles coincide, as do pairs of blue triangles. There are red-white pairs. How many white pairs coincide?
Small Hint:
Account for all red triangles first
Big Hint:
Then track how the unmatched blue triangles must pair
Solution:
Each half has red, blue, and white triangles.
The red-red pairs use red triangles from each half, so the remaining red triangle from each half is used in the red-white pairs. Thus all red triangles are accounted for.
The blue-blue pairs use blue triangles from each half, leaving blue triangles from each half. Since no more blue-blue pairs occur, those blue triangles must pair with white triangles.
So on each half, white is used with red and whites are used with blue, leaving white triangles to pair with white triangles.
Thus, B is the correct answer.
25.
There are four-digit whole numbers that use each of the four digits and exactly once. Only one of these four-digit numbers is a multiple of another one. Which of the following is it?
Small Hint:
A multiple must be twice or three times a smaller permutation
Big Hint:
Divide each answer choice by or when possible
Solution:
A number in the , , or range cannot be multiplied by or more and remain one of the given four-digit permutations. So the smaller number must start with , and the larger number must be either double or triple it.
For doubles, only answer choices ending in can work. But and , neither of which uses exactly the digits .
For triples, the possible answer choices are those divisible by : . Dividing gives , and only uses exactly the required digits.
Therefore is the unique listed multiple.
Thus, D is the correct answer.