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 300300 dimples on a golf ball. If it takes him 22 seconds to paint one dimple, how many minutes will he need to do his job?

44

66

88

1010

1212

Concepts:rateunit conversion
Difficulty rating: 370
Small Hint:

Convert the total painting time to seconds first

Big Hint:

There are 6060 seconds in one minute

Solution:

It will take Casey 2300=6002\cdot300=600 seconds to do the job. Since 6060 seconds make one minute, this is 600÷60=10600\div60=10 minutes.

Thus, D is the correct answer.

2.

I’m thinking of two whole numbers. Their product is 2424 and their sum is 11.11. What is the larger number?

33

44

66

88

1212

Difficulty rating: 450
Small Hint:

List the factor pairs of 2424

Big Hint:

Find the pair whose sum is 1111

Solution:

The factor pairs of 2424 are (1,24),(1,24), (2,12),(2,12), (3,8),(3,8), and (4,6)(4,6).

The only pair with sum 1111 is (3,8)(3,8), so the larger number is 88.

Thus, D is the correct answer.

3.

Granny Smith has $63.\$63. Elberta has $2\$2 more than Anjou and Anjou has one-third as much as Granny Smith. How many dollars does Elberta have?

1717

1818

1919

2121

2323

Concepts:fraction
Difficulty rating: 560
Small Hint:

Find one-third of Granny Smith’s money

Big Hint:

Elberta has $2\$2 more than Anjou

Solution:

Anjou has $63÷3=$21\$63\div3=\$21. Elberta has $2\$2 more than Anjou, so Elberta has $21+$2=$23\$21+\$2=\$23.

Thus, E is the correct answer.

4.

The digits 1,1, 2,2, 3,3, 4,4, and 99 are each used once to form the smallest possible even five-digit number. The digit in the tens place is

11

22

33

44

99

Difficulty rating: 720
Small Hint:

The number must end in 22 or 44

Big Hint:

Make the earlier digits as small as possible

Solution:

The units digit must be 22 or 44. If it is 22, arranging the remaining digits as small as possible gives 1349213492. If it is 44, the smallest arrangement is 1239412394, which is smaller. Therefore the smallest even number is 1239412394, whose tens digit is 99.

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 10881088 feet per second and one mile is 52805280 feet. Estimate, to the nearest half-mile, how far Snoopy was from the flash of lightning.

11

1121\frac{1}{2}

22

2122\frac{1}{2}

33

Difficulty rating: 730
Small Hint:

Use distance equals rate times time

Big Hint:

Compare the distance with 22 miles

Solution:

In 1010 seconds, the thunder was able to travel 101088=1088010 \cdot 1088 = 10880 feet.

Note that 22 miles is about 25280=105602 \cdot 5280 = 10560 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 6060 feet. What is the distance in feet between the first and last trees?

9090

100100

105105

120120

140140

Difficulty rating: 820
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 33 gaps between the first and fourth trees, which means that one gap is 60÷3=2060 \div 3 = 20 feet long.

There are 55 gaps between the first and last trees. This means that they are 520=1005 \cdot 20 = 100 feet apart.

Thus, B is the correct answer.

7.

Problems 7,7, 8,8, and 99 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?

2121

2222

2323

2424

2525

Difficulty rating: 900
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 2.2.

Therefore, the area of the small kite is 672=422=21. \dfrac{6 \cdot 7}{2} = \dfrac{42}{2} = 21.

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?

3030

3232

3535

3838

3939

Difficulty rating: 960
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 77 units, and the short one is 66 units.

In the large kite, one unit is 33 inches, so the total amount of bracing material needed is 3(7+6)=313=39. 3(7 + 6) = 3 \cdot 13 = 39.

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?

6363

7272

180180

189189

264264

Difficulty rating: 1020
Small Hint:

Tripling both dimensions multiplies area by 99

Big Hint:

The waste area equals the large kite area

Solution:

The area of the entire grid would be 3736=378. 3 \cdot 7 \cdot 3 \cdot 6 = 378. The area of the kite is one-half this area from the formula for the area of the kite, so the wasted material is 378÷2=189.378 \div 2 = 189.

Thus, D is the correct answer.

10.

A collector offers to buy state quarters for 2000%2000\% of their face value. At that rate how much will Bryden get for his four state quarters?

$20\$20

$50\$50

$200\$200

$500\$500

$2000\$2000

Difficulty rating: 980
Small Hint:

Four quarters have face value $1\$1

Big Hint:

2000%2000\% means 2020 times face value

Solution:

Four state quarters have face value $1\$1.

Since 2000%=202000\%=20, the collector pays 2020 times face value, or $20\$20.

Thus, A is the correct answer.

11.

Points A,A, B,B, CC and DD have these coordinates: A(3,2),A(3,2), B(3,2),B(3,-2), C(3,2)C(-3,-2) and D(3,0).D(-3,0). What is the area of quadrilateral ABCD?ABCD?

1212

1515

1818

2121

2424

Difficulty rating: 1140
Small Hint:

View ABCDABCD as a trapezoid

Big Hint:

The parallel vertical sides have lengths 44 and 22

Solution:

We can see that ABCDABCD is a trapezoid since DCAB.\overline{DC} \parallel \overline{AB}.

Recall that the formula for the area of a trapezoid is A=12(b1+b2)h. A = \dfrac{1}{2} (b_1 + b_2) h.

Plugging in b1=DC=2, b_1 = DC = 2, b2=AB=4, b_2 = AB = 4, and h=CB=6, h = CB = 6, we get that A=12(2+4)6 A = \dfrac{1}{2} (2 + 4) \cdot 6 =1266=18.= \dfrac{1}{2} \cdot 6 \cdot 6 = 18.

Thus, C is the correct answer.

12.

If ab=a+bab,a \otimes b = \dfrac{a + b}{a - b}, then (64)3=(6 \otimes 4) \otimes 3 =

44

1313

1515

3030

7272

Difficulty rating: 1170
Small Hint:

Evaluate 646\otimes4 first

Big Hint:

Then use the result as the first input with 33

Solution:

We can evaluate it as follows (64)3=6+4643=53=5+353=4. \begin{align*} (6 \otimes 4) \otimes 3 &= \dfrac{6 + 4}{6 - 4} \otimes 3 \\ &= 5 \otimes 3 \\&= \dfrac{5 + 3}{5 - 3} \\&= 4. \end{align*}

Thus, A is the correct answer.

13.

Of the 3636 students in Richelle’s class, 1212 prefer chocolate pie, 88 prefer apple, and 66 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?

1010

2020

3030

5050

7272

Difficulty rating: 1190
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 361286=10. 36 - 12 - 8 - 6 = 10. Half of these like cherry pie, which is 10÷2=5.10 \div 2 = 5.

The number of degrees for cherry pie would then be 360536=510=50. 360^{\circ} \cdot \dfrac{5}{36} = 5 \cdot 10^{\circ} = 50^{\circ}.

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

44

2424

7272

8080

144144

Difficulty rating: 1270
Small Hint:

Choose the two vegetables as an unordered pair

Big Hint:

Multiply meat choices, vegetable pairs, and dessert choices

Solution:

He has 33 choices for the meat and 44 choices for dessert.

He must choose 22 of the 44 vegetables. Since order does not matter, there are 432=6\dfrac{4\cdot3}{2}=6 vegetable choices.

This gives 364=723\cdot6\cdot4=72 possible meals.

Thus, C is the correct answer.

15.

Homer began peeling a pile of 4444 potatoes at the rate of 33 potatoes per minute. Four minutes later Christen joined him and peeled at the rate of 55 potatoes per minute. When they finished, how many potatoes had Christen peeled?

2020

2424

3232

3333

4040

Concepts:rate
Difficulty rating: 1290
Small Hint:

Find how many potatoes remain when Christen starts

Big Hint:

After that, their combined rate is 88 per minute

Solution:

Homer had peeled 34=123 \cdot 4 = 12 potatoes by the time Christen joined him, leaving 4412=3244 - 12 = 32 potatoes.

Together, Homer and Christen peel 5+3=85 + 3 = 8 potatoes per minute, taking them 32÷8=432 \div 8 = 4 minutes to peel the rest.

In 44 minutes, Christen peeled 45=204 \cdot 5 = 20 potatoes.

Thus, A is the correct answer.

16.

A square piece of paper, 44 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?

13\dfrac{1}{3}

12\dfrac{1}{2}

34\dfrac{3}{4}

45\dfrac{4}{5}

56\dfrac{5}{6}

Difficulty rating: 1350
Small Hint:

After folding, the paper is a 4×24\times2 rectangle

Big Hint:

The small rectangles are 4×14\times1

Solution:

The square is folded in half to create a 4×24\times2 rectangle.

Cutting the folded paper in half parallel to the fold gives two small 4×14\times1 rectangles and one large 4×24\times2 rectangle.

The ratio of the perimeter of a small rectangle to the perimeter of the large rectangle is 2(4+1)2(4+2)=1012=56.\frac{2(4+1)}{2(4+2)}=\frac{10}{12}=\frac56.

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 K=1000\text{K}=1000). #123$100200300 \begin{array}{ccccc} \boldsymbol{\#} & 1 & 2 & 3 \\ \boldsymbol{\$} & 100 & 200 & 300 \end{array} 456785001K2K4K8K \begin{array}{cccccc} 4 & 5 & 6 & 7 & 8 \\ 500 & 1\text{K} & 2\text{K} & 4\text{K} & 8\text{K} \end{array} 910111216K32K64K125K \begin{array}{ccccc} 9 & 10 & 11 & 12 \\ 16\text{K} & 32\text{K} & 64\text{K} & 125\text{K} \end{array} 131415250K500K1000K \begin{array}{ccc} 13 & 14 & 15 \\ 250\text{K} & 500\text{K} & 1000\text{K} \end{array} Between which two questions is the percent increase of the value the smallest?

From 11 to 22

From 22 to 33

From 33 to 44

From 1111 to 1212

From 1414 to 1515

Concepts:percentage
Difficulty rating: 1380
Small Hint:

Most listed increases are doublings

Big Hint:

Compare the few increases that are not exactly 100%100\%

Solution:

Most of the listed increases are doublings, which are 100%100\% increases.

The exceptions among the answer choices are from 22 to 33, from 33 to 44, and from 1111 to 1212.

These percent increases are 300200200=50%\dfrac{300-200}{200}=50\%, 500300300=6623%\dfrac{500-300}{300}=66\dfrac23\%, and 1250006400064000\dfrac{125000-64000}{64000}, which is about 95%95\%.

The smallest is from question 22 to question 33.

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 5?5?

136\dfrac{1}{36}

118\dfrac{1}{18}

16\dfrac{1}{6}

1136\dfrac{11}{36}

13\dfrac{1}{3}

Difficulty rating: 1400
Small Hint:

The product is a multiple of 55 exactly when a die shows 55

Big Hint:

It is easier to count no die showing 55

Solution:

The only way for the product to be a multiple of 55 is if at least one of the rolls is 5.5.

We can do complementary counting. The probability that neither rolls is a 55 is 5656=2536. \dfrac{5}{6} \cdot \dfrac{5}{6} = \dfrac{25}{36}.

Therefore, the probability that at least one roll is a 55 is 12536=1136. 1 - \dfrac{25}{36} = \dfrac{11}{36}.

Thus, D is the correct answer.

19.

Car MM traveled at a constant speed for a given time. This is shown by the dashed line. Car NN traveled at twice the speed for the same distance. If Car NN’s speed and time are shown as a solid line, which graph illustrates this?

Difficulty rating: 1430
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 NN travels at twice the speed of car M,M, so it is represented by a point that is twice as high on the speed axis as car M.M.

Since car NN travels at the same distance as car MM but at a faster speed, it takes half the time to complete the trip.

Therefore, the line representing car NN’s speed is half the length of the line representing car MM’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 (M\text{M}), Quay (Q\text{Q}) and Shana (S\text{S}).

S,Q,M\text{S,Q,M}

Q,M,S\text{Q,M,S}

Q,S,M\text{Q,S,M}

M,S,Q\text{M,S,Q}

S,M,Q\text{S,M,Q}

Difficulty rating: 1520
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 K=Q.\text{K} = \text{Q}.

Marty knows that his score is higher than Kaleana’s, so M>K.\text{M} \gt \text{K}. Shana knows that her score is lower than Kaleana’s, so S<K.\text{S} \lt \text{K}.

Substituting Q\text{Q} for K,\text{K}, we get the following inequality: S<Q<M.\text{S} \lt \text{Q} \lt \text{M}.

Thus, A is the correct answer.

21.

The mean of a set of five different positive integers is 15.15. The median is 18.18. The maximum possible value of the largest of these five integers is

1919

2424

3232

3535

4040

Difficulty rating: 1550
Small Hint:

The five numbers sum to 7575

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 18.18. There are two numbers less than 1818 and two numbers greater than it.

The mean of the set is 15,15, so the sum of all the numbers is 515=75.5 \cdot 15 = 75. In order to maximize the largest number with this sum, the other numbers must be as small as possible.

The two numbers less than 1818 must be positive and distinct, so they must be 11 and 2.2.

The number immediately after 1818 must also be as small as possible, so it must be 19.19.

Therefore, the remaining number, the maximum possible value in the set, is 75121819=35. 75 - 1 - 2 - 18 - 19 = 35.

Thus, D is the correct answer.

22.

On a twenty-question test, each correct answer is worth 55 points, each unanswered question is worth 11 point and each incorrect answer is worth 00 points. Which of the following scores is NOT possible?

9090

9191

9292

9595

9797

Concepts:casework
Difficulty rating: 1550
Small Hint:

Check scores near 100100

Big Hint:

With 1919 correct answers, only two scores are possible

Solution:

With 2020 correct answers, the score is 100100.

With 1919 correct answers, the score is either 9595 or 9696, depending on whether the remaining question is incorrect or unanswered.

With 1818 correct answers, the remaining two questions can contribute 00, 11, or 22 points, giving 9090, 9191, or 9292.

Thus the listed scores 90,91,92,9590,91,92,95 are possible, while 9797 is not.

Thus, E is the correct answer.

23.

Points R,R, SS and TT are vertices of an equilateral triangle, and points X,X, YY and ZZ are midpoints of its sides. How many noncongruent triangles can be drawn using any three of these six points as vertices?

11

22

33

44

2020

Difficulty rating: 1650
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 2,2,22,2,2; equilateral with sides 1,1,11,1,1; small isosceles with sides 1,1,31,1,\sqrt3; and larger isosceles with sides 1,3,21,\sqrt3,2.

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 44 noncongruent triangles.

Thus, D is the correct answer.

24.

Each half of this figure is composed of 33 red triangles, 55 blue triangles and 88 white triangles. When the upper half is folded down over the centerline, 22 pairs of red triangles coincide, as do 33 pairs of blue triangles. There are 22 red-white pairs. How many white pairs coincide?

44

55

66

77

99

Difficulty rating: 1650
Small Hint:

Account for all red triangles first

Big Hint:

Then track how the unmatched blue triangles must pair

Solution:

Each half has 33 red, 55 blue, and 88 white triangles.

The 22 red-red pairs use 22 red triangles from each half, so the remaining red triangle from each half is used in the 22 red-white pairs. Thus all red triangles are accounted for.

The 33 blue-blue pairs use 33 blue triangles from each half, leaving 22 blue triangles from each half. Since no more blue-blue pairs occur, those 44 blue triangles must pair with white triangles.

So on each half, 11 white is used with red and 22 whites are used with blue, leaving 83=58-3=5 white triangles to pair with white triangles.

Thus, B is the correct answer.

25.

There are 2424 four-digit whole numbers that use each of the four digits 2,2, 4,4, 5,5, and 77 exactly once. Only one of these four-digit numbers is a multiple of another one. Which of the following is it?

57245724

72457245

72547254

74257425

75427542

Difficulty rating: 1680
Small Hint:

A multiple must be twice or three times a smaller permutation

Big Hint:

Divide each answer choice by 22 or 33 when possible

Solution:

A number in the 40004000, 50005000, or 70007000 range cannot be multiplied by 22 or more and remain one of the given four-digit permutations. So the smaller number must start with 22, and the larger number must be either double or triple it.

For doubles, only answer choices ending in 44 can work. But 57242=2862\frac{5724}{2}=2862 and 72542=3627\frac{7254}{2}=3627, neither of which uses exactly the digits 2,4,5,72,4,5,7.

For triples, the possible answer choices are those divisible by 33: 7245,7425,75427245,7425,7542. Dividing gives 2415,2475,25142415,2475,2514, and only 24752475 uses exactly the required digits.

Therefore 7425=324757425=3\cdot2475 is the unique listed multiple.

Thus, D is the correct answer.