2011 AMC 8 Problems
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1.
Margie bought apples at a cost of cents per apple. She paid with a -dollar bill. How much change did Margie receive?
Answer: E
Difficulty rating: 370
Solution:
The apples cost a total of cents, which equals This means that Margie received dollars in change.
Thus, E is the correct answer.
2.
Karl's rectangular vegetable garden is feet by feet, and Makenna's is feet by feet. Whose garden is larger in area?
Karl’s garden is larger by square feet.
Karl’s garden is larger by square feet.
The gardens are the same size.
Makenna’s garden is larger by square feet.
Makenna’s garden is larger by square feet.
3.
Extend the square pattern of shaded and unshaded square tiles by attaching a border of shaded tiles around the square. What is the ratio of shaded tiles to unshaded tiles in the extended pattern?
Answer: D
Difficulty rating: 720
Solution:
In the extended figure, there are shaded tiles and unshaded tiles. Therefore, the ratio of shaded tiles to unshaded tiles is
Thus, D is the correct answer.
4.
Here is a list of the numbers of fish that Tyler caught in nine outings last summer: Which statement about the mean, median, and mode is true?
median < mean < mode
mean < mode < median
mean < median < mode
median < mode < mean
mode < median < mean
Answer: C
Difficulty rating: 720
Solution:
To find these values more easily, we can get the following ordered list:
From this, we see that the mode is the median is and the mean is
Since we get that:
mean median mode.
Thus, C is the correct answer.
5.
What time was it minutes after the beginning of January
January at PM
January at PM
January at AM
January at AM
January at PM
Answer: D
Difficulty rating: 770
Solution:
The remainder when is divided by is This means that which means that minutes is the same as hours and minutes.
hours takes us to January so we get that we are hours and minutes into January
Thus, D is the correct answer.
6.
In a town of adults, every adult owns a car, a motorcycle, or both. If adults own cars and adults own motorcycles, how many of the car owners do not own a motorcycle?
Answer: D
Difficulty rating: 870
Solution:
We know that people own motorcycles, so people do not own motorcycles.
Thus, D is the correct answer.
7.
Each of the following four large congruent squares is subdivided into combinations of congruent triangles or rectangles and is shaded. What percent of the total area is shaded?
Answer: C
Solution:
The top left and the bottom right shaded regions are both a quarter of each square. The top right is one-eighth, and the bottom left is three-eights. Their combined area is
Therefore, the shaded regions combined equal the area of one square, so they are of the total area.
Thus, C is the correct answer.
8.
Bag A contains three chips labeled and Bag B contains three chips labeled and If one chip is drawn from each bag, how many different values are possible for the sum of the two numbers on the chips?
Answer: B
Difficulty rating: 900
Solution:
We can create a table to look at all the possible outcomes and their respective sums.
From this, we can see that there are distinct values that we can get.
Thus, B is the correct answer.
9.
Carmen takes a long bike ride on a hilly highway. The graph indicates the miles traveled during the time of her ride. What is Carmen's average speed for her entire ride in miles per hour?
Answer: E
Difficulty rating: 870
Solution:
Carmen travels miles in hours, so her average speed is miles per hour.
Thus, E is the correct answer.
10.
The taxi fare in Gotham City is for the first mile and additional mileage charged at the rate for each additional mile. You plan to give the driver a tip. How many miles can you ride for ?
Answer: C
Solution:
There is a guaranteed tip, so we can subtract that from the total, leaving This is greater than so we can subtract that and add miles to the total distance.
We now have to use for additional miles. per mile is the same as for mile. That means one can ride for more miles with this much money. This leaves a total of miles.
Thus, C is the correct answer.
11.
The graph shows the number of minutes studied by both Asha (left bar) and Sasha (right bar) in one week. On the average, how many more minutes per day did Sasha study than Asha?
Answer: A
Difficulty rating: 1020
Solution:
We can calculate the difference in average minutes by looking at the differences per day.
Starting with Monday, the differences between Sasha and Asha are and This is a total of minutes. Therefore, the average difference is
Thus, A is the correct answer.
12.
Angie, Bridget, Carlos, and Diego are seated at random around a square table, one person to a side. What is the probability that Angie and Carlos are seated opposite each other?
Answer: B
Difficulty rating: 960
Solution:
Consider that Angie's seat is chosen. Carlos has an equal probability of being in any of the other seats. Only one of them is opposite Angie, however. Therefore, the probability is
Thus, B is the correct answer.
13.
Two congruent squares, and have side length They overlap to form the by rectangle shown. What percent of the area of rectangle is shaded?
Answer: C
Difficulty rating: 1140
Solution:
We get that
This means that the area of is The area of is
which is
Thus, C is the correct answer.
14.
There are students at Colfax Middle School, where the ratio of boys to girls is There are students at Winthrop Middle School, where the ratio of boys to girls is The two schools hold a dance and all students from both schools attend. What fraction of the students at the dance are girls?
Answer: C
Difficulty rating: 1140
Solution:
The total number of girls is
There are students total, so the fraction of girls is
Thus, C is the correct answer.
15.
How many digits are in the product
16.
Let be the area of the triangle with sides of length and Let be the area of the triangle with sides of length and What is the relationship between and
Answer: C
Difficulty rating: 1340
Solution:
Since these triangles are isosceles, we can drop altitudes to create two congruent right triangles as shown in the diagram.
Using the Pythagorean theorem, we get that the altitude of the triangle with area equals Similarly, we get that the altitude of the triangle with area equals
With these altitudes, we can calculate the areas of the triangles. We get that Similarly,
Therefore,
Thus, C is the correct answer.
17.
Let and be whole numbers. If then what does equal?
Answer: A
Difficulty rating: 1140
Solution:
To find the desired exponents, note that all the bases are prime numbers. This means that finding the prime factorization will be helpful.
We get that
From this, it is clear that and ( since that makes the term equal ).
Therefore,
Thus, A is the correct answer.
18.
A fair six-sided die is rolled twice. What is the probability that the first number that comes up is greater than or equal to the second number?
Answer: D
Difficulty rating: 1310
Solution:
There are possible outcomes when rolling a die twice: the first number is greater than the second, both numbers are equal, or the first number is less than the second number. The first and third outcomes have the same probability since they are symmetric.
The second outcome has a chance of happening, since the first number can be anything, and the second number must equal the first number. The other two outcomes have a combined probability of This means that each outcome has a chance of happening.
The desired probability is the first outcome plus the second outcome, for a total probability of
Thus, D is the correct answer.
19.
How many rectangles are in this figure?
Answer: D
Difficulty rating: 1430
Solution:
We can split the figure into these regions to make it easier to count the rectangles.
The rectangles in this figure are and These form rectangles.
Thus, D is the correct answer.
20.
Quadrilateral is a trapezoid, and the altitude is What is the area of the trapezoid?
Answer: D
Difficulty rating: 1410
Solution:
We can drop the following altitudes to more easily find the area.
We can use the Pythagorean Theorem to get that and
We also know that so
Then the area of is
Thus, D is the correct answer.
21.
Students guess that Norb's age is and Norb says, "At least half of you guessed too low, two of you are off by one, and my age is a prime number." How old is Norb?
Answer: C
Difficulty rating: 1470
Solution:
The first part of the statement means that Norb's age is greater than
The second part means that Norb's age is either between and or between and
Since is prime and is not, Norb's age is
Thus, C is the correct answer.
22.
What is the tens digit of
Answer: D
Difficulty rating: 1520
Solution:
To find the tens digit, it is enough to track powers of modulo . Since , the last two digits repeat every four powers.
Because , we have . Thus the tens digit is .
Thus, D is the correct answer.
23.
How many -digit positive integers have four different digits, where the leading digit is not zero, the integer is a multiple of and is the largest digit?
Answer: D
Difficulty rating: 1690
Solution:
For a number to be divisible by the units digit must be either or
If the units digit is one of the other three digits must be The remaining two digits must be chosen from There are ways to choose the pair, and there are ways to arrange the three digits for a total of numbers.
If the units digit is there are ways to choose the thousands digit. There are ways to choose the other digits. This leaves a total of numbers for this case.
Combining both cases, we get the total number of such integers is
Thus, D is the correct answer.
24.
In how many ways can be written as the sum of two primes?
Answer: A
Solution:
For two numbers to add to an odd number, one of them must be odd and the other even. Thus the only even prime is so the other number is forced to be is not prime, however, so cannot be written as the sum of two primes.
Thus, A is the correct answer.
25.
A circle with radius is inscribed in a square and circumscribed about another square as shown. Which fraction is closest to the ratio of the circle's shaded area to the shaded area between the two squares?
Answer: A
Difficulty rating: 1660
Solution:
The circle's shaded area is equal to the area of the circle minus the area of the smaller square. The side length of the inner square can be calculated using the Pythagorean Theorem to get
Therefore, the area of the inner square is The circle's shaded area is then
The area of the outside square is so the shaded area between the two squares is
The desired fraction is
Thus, A is the correct answer.