GRE Math : Proportion / Ratio / Rate

Study concepts, example questions & explanations for GRE Math

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Example Questions

Example Question #41 : Proportion / Ratio / Rate

Carol ate 3 pancakes in 5 minutes. If she continues to eat at the same rate, how many whole pancakes can she eat in 24 minutes?

Possible Answers:

\dpi{100} \small 6

\dpi{100} \small 15

\dpi{100} \small 14

\dpi{100} \small 12

\dpi{100} \small 8

Correct answer:

\dpi{100} \small 14

Explanation:

If Carol ate 3 pancakes in 5 minutes, she can eat \dpi{100} \small \frac{3}{5} of a pancake every minute. \dpi{100} \small \frac{3}{5}\ pancakes\times 24\ minutes=14.4\ pancakes.

That means she ate 14 whole pancakes (and an additional 2/5 of another pancake).

Example Question #1123 : Gre Quantitative Reasoning

If 24 machines can make 5 devices in 30 minutes, how many hours will it take 4 machines to make 15 devices?

Possible Answers:

9 hours

5 hours

12 hours

3 hours

6 hours

Correct answer:

9 hours

Explanation:

Approach this problem with the following reasoning.

Unit of work done = number of workers * rate * time

In our case, we are given 24 "workers," able to make 5 "units of work," in 0.5 "time." The rate is not given, but can be solved for with our given information.

Units of work = 5

Number of workers = 24

Time = 0.5 hours (30 minutes)

Now, since we know the rate, which does not chage, we can solve for the new time when the number of machines is decreased and the number of devices is increased.

 Unit of work done = number of workers * rate * time

Example Question #1131 : Gre Quantitative Reasoning

Mario can solve  problems in  hours. At this rate, how many problems can he solve in  hours?

Possible Answers:

Correct answer:

Explanation:

The rate is given by amount of probems over time.

To find the amount of problems done in a given amount of time, mulitply the rate by the given amount of time.

We can combine our y terms and cancel our n terms to simplify.

Example Question #1132 : Gre Quantitative Reasoning

It takes Mary 45 minutes to completely frost 100 cupcakes, and it takes Benjamin 80 minutes to completely frost 110 cupcakes.  How many cupcakes can they completely frost, working together, in 1 hour?

Possible Answers:

Correct answer:

Explanation:

In this rate word problem, we need to find the rates at which Mary and Bejamin frost their respective cupcakes, and then sum their respective rates per hour. In one hour Mary frosts 133 cupcakes. (Note: the question specifies COMPLETELY frosted cupcakes only, so the fractional results here will need to be rounded down to the nearest integer.)  Benjamin frosts 82 cupcakes.

82 + 133=215

Example Question #548 : Arithmetic

If John can paint a house in  hours and Jill can paint a house in  hours, how long will it take for both John and Jill to paint a house together?

Possible Answers:

Correct answer:

Explanation:

This problem states that John can paint a house in  hours. That means in  hour he will be able to paint  of a house.

The problem also states that Jill can paint a house in  hours. This means that in  hour, Jill can paint  of a house.

If they are painting together, you simply add the rate at which the paint separately together to find the rate at which they paint together. This means in  hour, they can paint  of a house. Now to find the time that paint an entire house, we simply invert that fraction, meaning that to paint an entire house together it would take them   of an hour, or .

 

The general formula for solving these work problems is , where  is the amount of time it takes worker A to finish the job alone and  is the amount of time it would take worker B to finish the job alone.

Example Question #1133 : Gre Quantitative Reasoning

Half of a salad is lettuce. A third of it is tomatoes. The remainder is made of cucumbers. Which of the following is the ratio of lettuce to cucumbers in the salad?

Possible Answers:

Correct answer:

Explanation:

First, you need to compute the amount of cucumbers used for the salad. A whole salad can be represented as  (like ). Thus, you know:

First, simplify the part of the equation to the left of the equals sign:

Thus, the ratio of lettuce to cucumbers is:

This can be simplified by multiplying both sides by :

Example Question #2 : How To Find The Ratio Of A Fraction

One third of a diet bar is made of shredded fiber. Of the remaining portion, a third is made of apples and the remainder is made of soy. What is the ratio of shredded fiber to soy?

Possible Answers:

Correct answer:

Explanation:

We know that the bar could be represented as:

, where  represents . Now, we know that . The remaining apples and soy comprise  of the bar. Now, the apples are one third of that remaining . (This is italicized because it is very important. The common error will be to think that it they are one third of the whole bar.) So, we know apples then are:

Thus, we can compute the soy by subtracting that from the :

Now the ratio of fiber to soy is:

Multiply both factors by  to simplify:

Example Question #3 : How To Find The Ratio Of A Fraction

A pie is made up of   crust,  apples, and  sugar, and the rest is jelly. What is the ratio of crust to jelly?

Possible Answers:

Correct answer:

Explanation:

A pie is made up of   crust,  apples,  sugar, and the rest is jelly. What is the ratio of crust to jelly?

To compute this ratio, you must first ascertain how much of the pie is jelly. This is:

Begin by using the common denominator :

So, the ratio of crust to jelly is:

This can be written as the fraction:

, or 

Example Question #1132 : Gre Quantitative Reasoning

In a solution,  of the fluid is water,  is wine, and  is lemon juice. What is the ratio of lemon juice to water?

Possible Answers:

Correct answer:

Explanation:

This problem is really an easy fraction division. You should first divide the lemon juice amount by the water amount:

Remember, to divide fractions, you multiply by the reciprocal:

This is the same as saying: 

Example Question #1133 : Gre Quantitative Reasoning

If  and , what is the ratio of  to ?

Possible Answers:

Correct answer:

Explanation:

To find a ratio like this, you simply need to make the fraction that represents the division of the two values by each other. Therefore, we have:

Recall that division of fractions requires you to multiply by the reciprocal:

which is the same as:

This is the same as the ratio:

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