2011 AMC 8 Exam Solutions
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All of the real AMC 8 and AMC 10 problems in our complete solution collection are used with official permission of the Mathematical Association of America (MAA).
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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?
Solution:
The apples costed 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.
Solution:
The area of Karl's garden is The area of Makenna's garden is
The difference of these area is Therefore, Makenna's garden is larger than Karl's.
Thus, E is the correct answer.
3.
Extend the square pattern of colored and uncolored square tiles by attaching a border of colored tiles around the square. What is the ratio of colored tiles to uncolored tiles in the extended pattern?
Solution:
In the extended figure, there are colored tiles and uncolored tiles. Therefore, the ratio of colored tiles to uncolored 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
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 midnight on January
January at PM
January at PM
January at AM
January at AM
January at PM
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, motorcycle, or both. If adults own cars and adults own motorcycles, how many of the car owners do not own a motorcycle?
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 partially shaded. What percent of the total area is partially shaded?
Solution:
The top left and the bottom right shaded regions are both a quarter of each square. The top right is one-eight, 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 has three chips labeled and Bag B has 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?
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?
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 $ 2.40 for the first mile and additional mileage charged at the rate $ 0.20 for each additional mile. You plan to give the driver a $ 2 tip. How many miles can you ride for $ 10?
Solution:
There is a guaranteed $ 2 tip, so we can subtract that from the total, leaving $ 8. This is greater than $ 2.40, so we can subtract that and add miles to the total distance.
We now have $ 5.60 to use for additional miles. $ 0.20 per mile is the same as $ 2 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 (black bar) and Sasha (grey bar) in one week. On the average, how many more minutes per day did Sasha study than Asha?
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?
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?
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?
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
Solution:
To find the number of digits, we can try to express this number in terms of powers of
We get that
This shows that the desired number is followed by zeros, for a total of digits.
Thus, D is the correct answer.
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
Solution:
Since these triangle are isosceles, we can drop altitudes to create two congruent right triangles as shown in the diagram.
Using the Pythagorean theorem, we get that 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?
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, \begin{gather*} 2w + 3x + 5y + 7z \\ = 2 \cdot 2 + 3 \cdot 1 + 5 \cdot 0 + 7 \cdot 2 \\ = 21. \end{gather*}
Thus, A is the correct answer.
18.
A fair 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?
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 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?
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?
Solution:
We can drop the following altitudes to more easily find the area.
We can use the Pythagorean 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?
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
Solution:
Solution 1
To find the tens digit, we can simply find the tens digit when taking the number Since then
Solution 2
If we look at the tens digits of powers of we get and from there the pattern repeats.
This means that the tens digits repeat in periods of Since leaves a remainder of when divided by its tens digit will be
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?
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?
Solution:
For two numbers to add to an odd number, one of them must be odd and the other even. Thus 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 area between the two squares?
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 calculate using the Pythagorean Theorem to get
Therefore, the area of the inner square is The area of the circle's shaded area is then
The area of the outside square is so the area of the shaded area between the two squares is
The desired fraction is
Thus, A is the correct answer.