1989 AMC 8 Solutions
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All problems are used with official legal permission of the Mathematical Association of America (MAA).
1.
What is the value of
Small Hint:
Look for pairs of terms that combine into round numbers
Big Hint:
Pairing with with and so on, each pair sums to
Solution:
Pair the terms so each pair sums to : and
There are such pairs, so the total is
Thus, the correct answer is E .
2.
What is the value of
Small Hint:
Write each fraction as a decimal using its place value
Big Hint:
and
Solution:
Each fraction is a decimal in a different place: and
Adding these gives
Thus, the correct answer is D .
3.
Which of the following numbers is the largest?
Small Hint:
Give every number the same number of decimal places by appending zeros
Big Hint:
Compare digit by digit from the left; the hundredths place decides between the leading numbers
Solution:
Write each number with four decimal places:
Comparing from the left, has the largest hundredths digit, so is the largest.
Thus, the correct answer is A .
4.
Estimate to determine which of the following is closest to
Small Hint:
Round and to simple numbers
Big Hint:
Solution:
Round the numerator and denominator:
Since the value is closest to
Thus, the correct answer is E .
5.
What is the value of
Small Hint:
Follow the order of operations: parentheses first, then multiplication, then addition
Big Hint:
so the expression becomes
Solution:
Inside the parentheses, Then multiplication comes before addition, so
Finally,
Thus, the correct answer is D .
6.
If the markings on the number line shown are equally spaced, what is the number
Small Hint:
Count how many equal spaces lie between and
Big Hint:
There are spaces from to so each space is then count the spaces up to
Solution:
From to there are equal spaces, so each space is
The mark labeled is spaces from so
Thus, the correct answer is C .
7.
The value of quarters and dimes equals the value of quarters and dimes. What is
Small Hint:
First find the total value of quarters and dimes
Big Hint:
After using quarters, find how much value the remaining dimes must supply, then divide by ¢
Solution:
The value of quarters and dimes is
Ten quarters are worth so the dimes must supply That is dimes, so
Thus, the correct answer is D .
8.
What is the value of
Small Hint:
distribute it across the three fractions
Big Hint:
Solution:
Since distribute it over the sum:
This equals
Thus, the correct answer is E .
9.
There are boys for every girls in Ms. Johnson’s math class. If there are students in her class, what percent of them are boys?
Small Hint:
For every boys there are girls, so boys are out of every students
Big Hint:
Convert the fraction to a percent
Solution:
Boys make up out of every students, which is of the class. The total of students is not even needed.
As a percent,
Thus, the correct answer is C .
10.
How many degrees are in the smaller angle between the hour hand and the minute hand of a clock that reads seven o’clock?
Small Hint:
The hour marks split the clock face into equal angles
Big Hint:
Each hour mark is at seven o’clock the hands are marks apart the short way
Solution:
The numbers divide the clock into equal sections of each.
At seven o’clock the hands point to and which are sections apart the short way, giving
Thus, the correct answer is D .
11.
Which of the five “T-like shapes” would be symmetric to the one shown with respect to the dashed line?
Small Hint:
Two figures are symmetric across the dashed line when folding the paper along that line makes one land exactly on the other
Big Hint:
A reflection across a vertical line keeps top and bottom fixed but swaps left and right; track where the small corner square ends up and how the slanted strokes turn
Solution:
Two figures are symmetric with respect to the dashed line when folding the paper along that line makes one coincide with the other. Reflecting across the vertical dashed line swaps left and right while leaving top and bottom unchanged.
Under this reflection the small square in the top-left corner moves to the top-right corner, the straight crossbar reverses its slant, and the stem that points down and to the right must instead point down and to the left. Only one choice has all three of these features.
Thus, the correct answer is B .
12.
What is the value of
Small Hint:
Simplify the numerator and denominator separately
Big Hint:
and then divide
Solution:
The numerator is and the denominator is
Dividing gives
Thus, the correct answer is E .
13.
Which of the following is equal to
Small Hint:
Dividing the numerator and one factor of the denominator by the same number keeps the fraction unchanged
Big Hint:
To turn into divide by to keep the value equal, divide one factor of the denominator by as well
Solution:
To rewrite the numerator as divide it by To keep the fraction equal, divide the denominator by too, which means dividing one of its factors by
Dividing the factor by gives which equals the original. Each other choice changes the value by a factor of or
Thus, the correct answer is A .
14.
When placing each of the digits in exactly one of the boxes of this subtraction problem, what is the smallest difference that is possible?
Small Hint:
Make the three-digit number as small as possible and the two-digit number as large as possible
Big Hint:
The largest two-digit number from these digits uses and build the smallest three-digit number from the digits that remain
Solution:
The difference is smallest when the three-digit number (the top) is as small as possible and the two-digit number (subtracted) is as large as possible.
The largest two-digit number is using the digits and The smallest three-digit number from the remaining digits is So the smallest difference is
Thus, the correct answer is C .
15.
In parallelogram shown, what is the area of the shaded region
Small Hint:
The shaded region is the whole parallelogram with the triangle removed
Big Hint:
The parallelogram area is triangle has base and height
Solution:
The parallelogram has base and height so its area is
The unshaded triangle has base and height so its area is The shaded area is
Thus, the correct answer is D .
16.
In how many ways can be written as the sum of two primes?
more than
Small Hint:
is odd, so one of the two primes must be even
Big Hint:
The only even prime is which would force the other prime to be
Solution:
Since is odd, a sum of two primes equal to needs one even prime and one odd prime. The only even prime is
That would require the other number to be but is not prime. So there is no way.
Thus, the correct answer is A .
17.
The number is between and Which of the following could be the average of and
Small Hint:
The average is find its value at each end of the range for
Big Hint:
As runs from to the average runs from to
Solution:
The average is When this is and when it is
So the average lies strictly between about and Among the choices, only falls in this range.
Thus, the correct answer is B .
18.
A calculator has a reciprocal key that replaces the number currently displayed with its reciprocal. For example, if the display shows and the key is pressed, the display becomes If is currently displayed, what is the fewest number of times the reciprocal key must be pressed so that the display again reads
Small Hint:
Pressing the key once turns into
Big Hint:
The reciprocal of the reciprocal of a number is the number itself
Solution:
Pressing the key once changes to its reciprocal
Pressing it a second time takes the reciprocal again, returning to So presses are enough.
Thus, the correct answer is B .
19.
The graph below shows the total accumulated dollars (in millions) spent by the Surf City government during For example, about million had been spent by the beginning of February and approximately million by the end of April. Approximately how many millions of dollars were spent during the summer months of June, July, and August?
Small Hint:
Because the graph shows an accumulated total, the amount spent over a span of months is the increase in that total across the span
Big Hint:
Read the height of the curve at the beginning of June and at the end of August, then subtract the two values
Solution:
The graph gives the total accumulated spending, so the amount spent during June, July, and August equals the accumulated total at the end of August minus the accumulated total at the beginning of June.
The curve is at a bit more than million at the beginning of June and a bit more than million by the end of August. The difference is about million.
Thus, the correct answer is B .
20.
The figure shown may be folded along the lines to form a number cube. Three faces come together at each corner of the cube. What is the largest sum of three numbers whose faces come together at a corner?
Small Hint:
A corner uses three faces that are mutually adjacent, so no two of them can be opposite faces
Big Hint:
Folding the net, the opposite face pairs are & & and & take the larger of each pair
Solution:
When the net is folded, the pairs of opposite faces are and and and and Three faces meeting at a corner must come one from each opposite pair.
To maximize the sum, take the larger number from each pair: and These three faces do meet at a corner, and their sum is
Thus, the correct answer is D .
21.
Jack had a bag of apples. He sold of them to Jill. Next he sold of those remaining to June. Of those apples still in his bag, he gave the shiniest one to his teacher. How many apples did Jack have then?
Small Hint:
Selling leaves of the apples
Big Hint:
Multiply by twice, then subtract the one given to the teacher
Solution:
After selling to Jill, Jack keeps apples. After selling of those to June, he keeps apples.
He then gives to his teacher, leaving
Thus, the correct answer is D .
22.
The letters and the digits are each cycled separately (shifted one place at a time) to build a numbered list. Starting from AJHSME the list begins: line is JHSMEA line is HSMEAJ line is SMEAJH and so on. On what numbered line will AJHSME appear for the first time?
Small Hint:
The six letters return to AJHSME every lines; the four digits return to every lines
Big Hint:
Both return together on the least common multiple of and
Solution:
The six letters cycle back to their original order AJHSME every lines, and the four digits cycle back to every lines.
Both happen on the same line at the least common multiple of and which is So AJHSME first reappears on line
Thus, the correct answer is C .
23.
An artist has cubes, each with an edge of meter. She stands them on the ground to form a sculpture as shown. She then paints the exposed surface of the sculpture. How many square meters does she paint?
Small Hint:
Count the exposed faces on the four vertical sides, then the faces seen from directly above
Big Hint:
Each of the four sides shows exposed faces, and looking straight down covers the full footprint of top faces
Solution:
Because each higher layer is flush into one corner, each of the four vertical sides shows a stepped profile of exposed square faces, for side faces.
Viewed from directly above, the top faces cover the full footprint, adding more faces. The bottom rests on the ground and is not painted, so the total is square meters.
Thus, the correct answer is C .
24.
Suppose a square piece of paper is folded in half vertically. The folded paper is then cut in half along the dashed line. Three 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:
Give the original square a convenient side length, such as and track the pieces
Big Hint:
The piece containing the fold unfolds to a large rectangle, while each other layer is a small rectangle
Solution:
Let the square have side Folding in half makes a stack of two layers. Cutting parallel to the fold splits it into a strip containing the fold and a strip that does not.
The strip with the fold unfolds into the large rectangle, with perimeter The other strip is two separate small rectangles, each with perimeter The ratio is
Thus, the correct answer is E .
25.
Every time the two wheels shown are spun, two numbers are selected by the pointers. What is the probability that the sum of the two selected numbers is even?
Small Hint:
A sum is even exactly when both numbers are even or both are odd
Big Hint:
The first wheel has even and odd numbers; the second has even and odd
Solution:
The sum is even when both numbers are even or both are odd. The first wheel has evens and odds each with probability The second wheel has even with probability and odds with probability
So the probability of an even sum is
Thus, the correct answer is C .