Evaluating Expressions - GRE Quantitative Reasoning

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Question

Quantitative Comparison

A

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B

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Answer

Since both values are negative, in both situations the final result of the fraction will be positive regardless of the absolute value sign. Additionally, the definition of the exponent "–1" means the value is becoming its reciprocal. Thus, "x" → "1/x" and "1/y" → "y", equating to y/x.

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Question

Quantitative Comparison

0 < x < 1

A

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(2x + 5)/(x2)

B

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5x

Answer

Since A is a fraction with an exponential term in the denominator, its maximum value is when x is at a minimum. In B, the maximum value is when x approaches its maximum. Therefore, we can check whether there is overlap between the two quantities: No matter how close to either 0 or 1 x reaches, A will always be greater than B. (In fact, the minimum value for A is ~7, while the maximum value of B is ~5)

Be sure to keep your value of x consistent when plugging between the two fractions! The question asks for when they have the same x-value, not for when they are solved independently.

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Question

If x = -4 and y = 7, what is the value of 3x-5y?

Answer

Substitute the values into equation: 3(-4) - 5(7) = -12 - 35 = -47.

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Question

If the average (arithmetic mean) of the above terms is , what is the median?

Answer

Since we know the mean is 7, and the number of terms is 5, we can first find the value of x:

((x – 2)+ (x) + (x + 1) + (x + 4) + (x + 7))/5 = (5x + 10)/5 = 7

x = 5

Since the terms are already listed in order, we can simpy plug in x = 5 to the middle value to get 5 + 1 = 6 as the median term.

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Question

Quantitative Comparison

Quantity A: x

Quantity B: 2_x_

Answer

For a quantitative comparison question such as this one, it is best to first plug in the numbers 0, 1, and –1. Plugging in 0 gets the same answer for both columns. Plugging in 1 makes Quantity B bigger. Plugging in –1 makes Quantity A bigger. Therefore the answer cannot be determined.

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Question

A store sells 17 coffee mugs for $169. Some of the mugs are $12 each and some are $7 each. How many $7 coffee mugs were sold?

Answer

The answer is 7.

Write two independent equations that represent the problem.

x + y = 17 and 12_x_ + 7_y_ = 169

If we solve the first equation for x, we get x = 17 – y and we can plug this into the second equation.

12(17 – y) + 7_y_ = 169

204 – 12_y_ + 7_y_ =169

–5_y_ = –35

y = 7

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Question

How many square tiles, each with an area of 49 square inches, must be used to completely cover a floor with a width of 98 inches and a length of 49 inches.

Answer

The answer is 98.

If the area of each square tile is 49 then each side of the tile is 7. The width of the floor is 98 so 14 tiles would fit across. The length of the floor is 49 so 7 tiles would fit down.

14 tiles * 7 tiles = 98 tiles total

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Question

Kim has 22 coins made up of quarters, nickles, and dimes that total $2.45. Kim has twice as many nickles as quarters. How many dimes does she have?

Answer

The answer is 7.

Let us first write down three equations that represent the problem:

n + d + q = 22

2_q_ = n

5_n_ + 10_d_ + 25_q_ = 245

Lets plug the second equation into the first and third equations:

(2_q)_ + d + q = 22

5(2_q_) + 10_d_ + 25_q_ = 245

Solve the first equation for d and plug into the last equation:

d = 22 – 3_q_

10q + 10(22 – 3_q_) + 25_q_ = 245

Solve for q.

220 – 30_q_ + 25_q_ + 10_q_ = 245

5_q_ = 25

q = 5

Therefore, n = 10 and d = 7

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Question

In the equation ax + b = 32, x is a constant. If a = 3 when b = 2, what is a when b = 12?

Answer

The answer is 2.

First solve for the constant x:

3_x_ + 2 = 32

x = 10

Now plug in x = 10 and b = 12:

a(10) + 12 = 32

a = 2

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Question

A specialty socket wrench, typically priced at $29.99, is on sale for 30% off. An additional 45% is discounted at the register. What is the final sale price of the wrench?

Answer

The answer is $11.55

The original cost is $29.99 but we are going to discount 30%, meaning we will only pay 70%. The new prices is 29.99 x 0.70 = $20.99.

The new price is then dicounted an additional 45%, meaning we will only pay 55% of the new price. The final price is 20.99 x 0.55 = $11.55.

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Question

Quantitative Comparison

x is an integer.

Quantity A: (x + 1)2

Quantity B: (x – 1)2

Answer

When picking numbers, we should always try to plug in the numbers 0, 1, and –1 first.

First try 0:

(0 + 1)2 = 1

(0 – 1)2 = 1

Here the two quantities are equal.

Now try 1:

(1 + 1)2 = 4

(1 – 1)2 = 0.

Here Quantity A is greater.

Therefore the relationship cannot be determined.

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Question

Barry's workout today consists of 10 squats every minute on the minute and 6 situps every other minute for 1 hour. How many squats and situps does Barry do in total?

Answer

squats: 10 squats * 60 minutes = 600 squats

situps: 6 situps * 30 minutes = 180 situps

total = 600 + 180 = 780

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Question

Quantitative Comparison

Quantity A:

Quantity B:

Answer

If x = 0, (x – 5)2 = 25 and (x + 5)2 = 25, so the quantities are equal.

If x = 1, (x – 5)2 = (–4)2 = 16 and (x + 5)2 = 62 = 36, so B is greater.

This is a contradiction, so the answer cannot be determined.

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Question

Fran has eight more chickens that Jan. If Fran gives two of her chickens to Jan, Fran will have twice as many chickens as Jan. How many chickens does Fran currently have (before giving two away to Jan)?

Answer

Set up two different equations:

and

Note the importance in the second equation of accounting for the exchange of 2 chickens for both quantities: Jan loses the two that she gives to Fran, and Fran gains the two that she receives.

Solve for by substituting for \dpi{100} \small j in the second equation:

Solving for results in .

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Question

Let and be integers such that and .

Quantity A Quantity B

0

Answer

The quantity produces a minimum of and a maximum of 4, which are less than and greater than 0, respectively. Therefore, the answer cannot be determined from the information given.

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Question

Let be a positive integer such that one less than three-eighths of is the third prime integer. What is the value of ?

Answer

The third prime integer is 5, since 1 is not considered a prime number.

Working backwards,

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Question

\dpi{100} \small -3x-5y=10

\dpi{100} \small 4x+6y=25

Quantity A Quantity B

35 \dpi{100} \small x+y

Answer

You don't actually need to solve for the values of x and y. You just want to know the sum of x and y. Adding the two equations together you get

\dpi{100} \small -3x-5y=10

\dpi{100} \small +4x+6y=25

_________________

\dpi{100} \small x+y=35

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Question

In a four-digit positive interger \dpi{100} \small y, the thousand's digit is three times the units digit.

Quantitiy A Quantitiy B

Unit's digit of \dpi{100} \small y 4

Answer

If we set the quantities equal, and the units digit of \dpi{100} \small y is 4, then the thousands digit which is three times the units digit would be 12, which doesnt make sense at all because a digit must be one of the integers 0 through 9. So 4 is too big to be the units digit of \dpi{100} \small y. Therefore Quantity B is greater.

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Question

The arithmetic mean of \dpi{100} \small 5,\ x,\ x+2,\ 7,\ and \ 8 is 6. What is the value of \dpi{100} \small x?

Answer

The arithmetic mean is the sum of all numbers in a series divided by the number of items in the series. There are 5 items in the series, so they must sum to\dpi{100} \small 6\times 5 = 30.

If we subtract \dpi{100} \small 5+7+8 from \dpi{100} \small 30, you are left with \dpi{100} \small 10 so therefore \dpi{100} \small x+2+x must sum to \dpi{100} \small 10.

\dpi{100} \small x+2+x=10

\dpi{100} \small 2x +2=10

\dpi{100} \small 2x=8

\dpi{100} \small x=4

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Question

If \dpi{100} \small a+b=5, \dpi{100} \small b+c=10 and \dpi{100} \small a+c=8, what is the value of \dpi{100} \small a+b+c?

Answer

If you add all three equations together you get \dpi{100} \small a+b+b+c+a+c=5+10+8

\dpi{100} \small 2a+2b+2c=23

\dpi{100} \small a+b+c=\frac{23}{2}=11.5

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