2022 AMC 8 Solutions
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All problems are used with official legal permission of the Mathematical Association of America (MAA).
1.
The Math Team designed a logo shaped like a multiplication symbol, shown below on a grid of -inch squares. What is the area of the logo in square inches?
Small Hint:
Break the logo into congruent tilted squares
Big Hint:
Each tilted square is half of a by grid square
Solution:
The logo is made from congruent tilted squares. Each tilted square has both diagonals of length , so its area is square inches.
The total area is .
Thus, the correct answer is A.
2.
Consider these two operations:
Compute the value:
Small Hint:
Evaluate first
Big Hint:
Substitute the value from the first operation into
Solution:
Using the definitions,
Thus, the correct answer is D.
3.
When three positive integers and are multiplied together, their product is Suppose In how many ways can the numbers be chosen?
Small Hint:
The smallest number must be a factor of
Big Hint:
Try possible values of with
Solution:
Since and , we have , so . Also must divide , so .
If , the pairs are . If , the only possible pair is . If , then , and there is no integer with .
There are possible triples.
Thus, the correct answer is E.
4.
The letter M in the figure below is first reflected over the line and then reflected over the line What is the resulting image?
Small Hint:
Reflecting over moves the letter across the diagonal line
Big Hint:
After the first reflection, reflect the new image over the horizontal line
Solution:
Reflecting over the diagonal line changes the orientation of the letter as if the diagonal were a mirror. Reflecting that image over the horizontal line then places the final letter below , to the right of the vertical line, with the orientation shown in choice E.
Thus, the correct answer is E.
5.
Anna and Bella are celebrating their birthdays together. Five years ago, when Bella turned years old, she received a newborn kitten as a birthday present. Today the sum of the ages of the two children and the kitten is years. How many years older than Bella is Anna?
Small Hint:
Bella is years older now than when she turned
Big Hint:
Find Bella’s current age and the kitten’s current age before finding Anna’s
Solution:
If Bella was five years ago, then she is right now.
If the kitten was a newborn five years ago, then it is right now.
Since the sum of all ages is Anna’s age is
Since Anna is and Bella is she is years older than Bella.
Thus, the correct answer is C.
6.
Three positive integers are equally spaced on a number line. The middle number is and the largest number is times the smallest number. What is the smallest of these three numbers?
Small Hint:
The middle of three equally spaced numbers is their average
Big Hint:
If the smallest is , then the largest is
Solution:
Let the smallest number be . Then the largest is . Since the three numbers are equally spaced, the middle number is the average of the smallest and largest: Thus , so .
Thus, the correct answer is C.
7.
When the World Wide Web first became popular in the 1990s, download speeds reached a maximum of about kilobits per second. Approximately how many minutes would the download of a -megabyte song have taken at that speed? (Note that there are kilobits in a megabyte.)
Small Hint:
Convert megabytes to kilobits first
Big Hint:
kilobits divided by kilobits per second gives seconds
Solution:
The song has kilobits. At kilobits per second, the download takes seconds, which is minutes.
Thus, the correct answer is B.
8.
What is the value of:
Small Hint:
Most numerator and denominator factors cancel
Big Hint:
After cancellation, only remains on top
Solution:
Since every integer from to occurs once as a denominator and once as a numerator, they cancel each other out.
After canceling every number out, we have only and left as numerators and and left as denominators.
The remaining fraction is This simplifies to
Thus, the correct answer is B.
9.
A cup of boiling water ( F) is placed to cool in a room whose temperature remains constant at F. Suppose the difference between the water temperature and the room temperature is halved every minutes. What is the water temperature, in degrees Fahrenheit, after minutes?
Small Hint:
Track the difference from room temperature
Big Hint:
In minutes, the difference is halved times
Solution:
The current difference is
Since we have minutes while halving every minutes, we halve the difference times.
This means the difference is multiplied by so our new difference is This makes our final temperature
Thus, the correct answer is B.
10.
One sunny day, Ling decided to take a hike in the mountains. She left her house at a.m., drove at a constant speed of miles per hour, and arrived at the hiking trail at a.m. After hiking for hours, Ling drove home at a constant speed of miles per hour. Which of the following graphs best illustrates the distance between Ling’s car and her house over the course of her trip?
Small Hint:
Find the distance to the trail from the first drive
Big Hint:
The return drive is faster, so it takes less time than the outward drive
Solution:
She drives miles per hour for hours, so the trail is miles from her house. The graph must rise from to miles between AM and AM, then stay flat for the -hour hike.
She starts home at PM. Driving miles at miles per hour takes hours, so she gets home at PM. This matches choice E.
Thus, the correct answer is E.
11.
Henry the donkey has a very long piece of pasta. He takes a number of bites of pasta, each time eating inches of pasta from the middle of one piece. In the end, he has pieces of pasta whose total length is inches. How long, in inches, was the piece of pasta he started with?
Small Hint:
Each bite increases the number of pasta pieces by
Big Hint:
To end with pieces, Henry made bites
Solution:
Since there are pieces, there were locations where a bite was made. Since we have bites and inches are removed per bite, a total of inches were removed.
With inches removed and inches remaining, we know we started with inches.
Thus, the correct answer is D.
12.
The arrows on the two spinners shown below are spun. Let the number equal times the number on Spinner A, added to the number on Spinner B. What is the probability that is a perfect square number?
Small Hint:
Spinner A gives the tens digit and spinner B gives the ones digit
Big Hint:
Check which two-digit squares have tens digit and ones digit
Solution:
Spinner A gives the tens digit and Spinner B gives the ones digit. There are equally likely two-digit numbers.
The possible perfect squares between and are and , and both can occur. Thus the probability is
Thus, the correct answer is B.
13.
How many positive integers can fill the blank in the sentence below?
“One positive integer is ___ more than twice another, and the sum of the two numbers is ”
Small Hint:
Let the smaller of the two positive integers be
Big Hint:
If the blank is , the two numbers can be and
Solution:
Let the smaller number be , and let the blank be . Then the other number is , where both and are positive integers.
The sum condition gives , so . For to be positive, , so .
Thus can be any integer from through , giving possible values of the blank.
Thus, the correct answer is D.
14.
In how many ways can the letters in BEEKEEPER be rearranged so that two or more E’s do not appear together?
Small Hint:
There are E’s and other letters
Big Hint:
The four non-E letters must fill the four gaps between the E’s
Solution:
The word has E’s and other letters: B, K, P, and R. To keep no two E’s adjacent, the only possible pattern is with the four non-E letters in the four gaps.
The letters B, K, P, and R can be arranged in those gaps in ways.
Thus, the correct answer is D.
15.
Laszlo went online to shop for black pepper and found thirty different black pepper options varying in weight and price, shown in the scatter plot below. In ounces, what is the weight of the pepper that offers the lowest price per ounce?
Small Hint:
Compare price divided by weight
Big Hint:
For each weight, only the lowest plotted price can be best
Solution:
For each weight, only the lowest-price point at that weight can give the lowest price per ounce.
At ounce, the lowest price is more than dollar, so the price per ounce is more than .
At ounces, the lowest price is dollars, so the price per ounce is .
At ounces, the lowest price is about dollars, so the price per ounce is about , less than .
At ounces, the lowest price is close to dollars, so the price per ounce is close to , still larger than the -ounce option.
At ounces, the lowest price is close to dollars, so the price per ounce is close to , also larger than the -ounce option.
The price per ounce is lowest at ounces.
Thus, the correct answer is C.
16.
Four numbers are written in a row. The average of the first two is the average of the middle two is and the average of the last two is What is the average of the first and last of the numbers?
Small Hint:
Convert each average into a sum
Big Hint:
Find , then subtract
Solution:
Let the numbers be in order.
Since the average of and is we know their sum is
Since the average of and is we know their sum is
Since and we know
Now, with the average of and being we know their sum is This means
Subtracting this result from the sum of all the terms yields
Since our answer is
Thus, the correct answer is B.
17.
If is an even positive integer, the double factorial notation represents the product of all the even integers from to For example:
What is the units digit of the following sum?
Small Hint:
Any even double factorial at least has a factor of
Big Hint:
Only and can affect the units digit
Solution:
For every even the product contains a factor of so that term has units digit Only the first four terms can affect the units digit.
They sum to Therefore the full sum has units digit
Thus, the correct answer is B.
18.
The midpoints of the four sides of a rectangle are and What is the area of the rectangle?
Small Hint:
The given midpoints form a parallelogram inside the rectangle
Big Hint:
The midpoint parallelogram has half the area of the original rectangle
Solution:
The four given midpoints form a parallelogram. Its horizontal base has length , and its height is , so its area is .
For any rectangle, the parallelogram formed by joining the side midpoints has half the area of the rectangle. Therefore the rectangle’s area is .
Thus, the correct answer is C.
19.
Mr. Ramos gave a test to his class of students. The dot plot below shows the distribution of test scores.
Later Mr. Ramos discovered that there was a scoring error on one of the questions. He regraded the tests, awarding some of the students extra points, which increased the median test score to What is the minimum number of students who received extra points?
(Note that the median test score equals the average of the scores in the middle if the test scores are arranged in increasing order.)
Small Hint:
The median is controlled by the th and th scores
Big Hint:
Count how many scores are at least before and after regrading
Solution:
All scores are multiples of and adding preserves that fact. If the th and th scores average but are not both then the th score must be at least That would require at least scores of or more.
However, even after regrading, only the original scores of or more can reach The plot has only such scores, so the two middle scores must both be
The plot initially has scores of at least To make the th and th scores both there must be at least scores of at least Raising four of the ’s to is both necessary and sufficient.
Thus, the correct answer is C.
20.
The grid below is to be filled with integers in such a way that the sum of the numbers in each row and the sum of the numbers in each column are the same. Four numbers are missing. The number in the lower left corner is larger than the other three missing numbers. What is the smallest possible value of
Small Hint:
The completed row and column sums must match the top row
Big Hint:
Express the other missing entries in terms of
Solution:
Adding the numbers in the top row shows that every row and column must have sum .
In the first column, the missing number above is . In the bottom row, the missing number to the right of is . In the middle row, the remaining missing number is .
Since is larger than the other missing numbers, we need , , and . The strongest condition is , so the smallest possible integer value is .
Thus, the correct answer is D.
21.
Steph scored baskets out of attempts in the first half of a game, and baskets out of attempts in the second half. Candace took attempts in the first half and attempts in the second. In each half, Steph scored a higher percentage of baskets than Candace. Surprisingly they ended with the same overall percentage of baskets scored. How many more baskets did Candace score in the second half than in the first?
Small Hint:
Steph made baskets in attempts overall
Big Hint:
Candace must also have made baskets total
Solution:
Steph made baskets in attempts. Candace also took attempts, and their overall percentages were the same, so Candace also made baskets.
Let be Candace’s first-half baskets and be her second-half baskets. Then .
Steph’s first-half percentage was , so , giving . Steph’s second-half percentage was , so .
Thus and . Since , the only possibility is and , so .
Thus, the correct answer is C.
22.
A bus takes minutes to drive from one stop to the next, and waits minute at each stop to let passengers board. Zia takes minutes to walk from one bus stop to the next. As Zia reaches a bus stop, if the bus is at the previous stop or has already left the previous stop, then she will wait for the bus. Otherwise she will start walking toward the next stop. Suppose the bus and Zia start at the same time toward the library, with the bus stops behind. After how many minutes will Zia board the bus?
Small Hint:
Check Zia’s decision only when she reaches a stop
Big Hint:
Compare positions at , , and minutes
Solution:
The bus takes minutes to drive to the next stop and then waits minute, so it moves through one-stop cycles every minutes.
Zia makes a decision only when she reaches a stop, every minutes. Measure stops from the bus’s starting stop. Zia starts at stop .
After minutes, Zia is at stop , while the bus is waiting at stop , so she keeps walking. After minutes, Zia is at stop , while the bus is between stops and , so she keeps walking. After minutes, Zia is at stop , while the bus is at stop , the previous stop, so she waits.
The bus then takes more minutes to reach her stop, so she boards after minutes.
Thus, the correct answer is A.
23.
A or is placed in each of the nine squares in a grid. Shown below is a sample configuration with three ’s in a line.
How many configurations will have three ’s in a line and three ’s in a line?
Small Hint:
Split by how many triangles are in the grid
Big Hint:
With exactly triangles, diagonal triangle lines do not work
Solution:
Let be the number of triangles. To have both a triangle line and a circle line, we need .
If , the three triangles must form a line. A row or column works, because the remaining six circles contain a full circle row or column. A diagonal does not work, because its complement contains no full line of circles. Thus there are configurations for . By symmetry, there are also configurations for .
If , choose the triangle line and then the extra triangle. If the line is a row or column, all possible extra positions work, because one parallel row or column remains all circles. This gives configurations. If the triangle line is a diagonal, no extra position leaves a full circle line. By symmetry, also gives configurations.
The total number of configurations is .
Thus, the correct answer is D.
24.
The figure below shows a polygon consisting of rectangles and right triangles. When cut out and folded on the dotted lines, the polygon forms a triangular prism. Suppose that:
and
What is the volume of the prism?
Small Hint:
Find the right-triangle base of the prism
Big Hint:
The folded net gives a base with legs and , and prism length
Solution:
When the net is folded, the matching side lengths give . Since is a rectangle, . The fold identifies with , so . In rectangle , this gives , and the opposite side equals .
Since , we have . Thus one triangular base of the prism is right triangle , with area The prism length is , so the volume is .
Thus, the correct answer is C.
25.
A cricket randomly hops between leaves, on each turn hopping to one of the other leaves with equal probability. After hops, what is the probability that the cricket has returned to the leaf where it started?
Small Hint:
Track only whether the cricket is on the starting leaf
Big Hint:
If the cricket is not at the start, the next hop returns with probability
Solution:
Let be the probability that the cricket is on its starting leaf after hops. We have .
If the cricket is on the starting leaf, the next hop must leave it. If the cricket is not on the starting leaf, exactly one of the possible hops returns to the start. Therefore
Thus
Thus, the correct answer is E.