GMAT Math : Calculating ratio and proportion

Study concepts, example questions & explanations for GMAT Math

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Example Questions

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Example Question #1 : Calculating Ratio And Proportion

The ratio 4 to \frac{1}{4} is equal to which of the following ratios?

Possible Answers:

\dpi{100} \small 12 to \dpi{100} \small 1

\dpi{100} \small 8 to \dpi{100} \small 1

\dpi{100} \small 16 to \dpi{100} \small 1

\dpi{100} \small 6 to \dpi{100} \small 1

\dpi{100} \small 16 to \dpi{100} \small 3

Correct answer:

\dpi{100} \small 16 to \dpi{100} \small 1

Explanation:

The ratio \dpi{100} \small 4 to \frac{1}{4} is equal to \frac{4}{\frac{1}{4}} which is  4\left ( \frac{4}{1} \right )= 16.

\dpi{100} \small 16 can be written as the ratio \dpi{100} \small 16 to \dpi{100} \small 1.

Example Question #2 : Calculating Ratio And Proportion

The annual budget for a road construction project is $25,200 budgeted equally over 12 months. If by the end of the third month the actual expenses have been $7,420, how much has the construction project gone over budget?

Possible Answers:

\dpi{100} \small \$3340

\dpi{100} \small \$ 980

\dpi{100} \small \$2150

\dpi{100} \small \$1640

\dpi{100} \small \$ 1120

Correct answer:

\dpi{100} \small \$ 1120

Explanation:

The monthly budget is found by:

\frac{25,200}{12}=2,100

which for 3 months is a budget of:

2,100\cdot 3= 6,300

To find out how much they are over budget the budgeted amount is subtracted from the actual expenses.
7,420 - 6,300 = 1,120

Example Question #3 : Calculating Ratio And Proportion

The ratio \dpi{100} \small 3 to \dpi{100} \small \frac{1}{2} is equal to the ratio:

Possible Answers:

\dpi{100} \small 3\ to\ 2

\dpi{100} \small 6\ to\ 1

\dpi{100} \small 5\ to\ 1

\dpi{100} \small 1\ to\ 6

\dpi{100} \small 2\ to\ 3

Correct answer:

\dpi{100} \small 6\ to\ 1

Explanation:

The ratio \dpi{100} \small 3 to \dpi{100} \small \frac{1}{2} is the same as \dpi{100} \small \frac{3}{\frac{1}{2}}=3\times \frac{2}{1}=6,
which equals a ratio of \dpi{100} \small 6 to \dpi{100} \small 1.

Also, if you double both sides of the ratio, you get \dpi{100} \small 6 to \dpi{100} \small 1

Example Question #4 : Calculating Ratio And Proportion

Nishita has necklaces, bracelets, and rings in a ratio of 7:5:4. If she has 64 jewelry items total, how many bracelets does she have?

Possible Answers:

Correct answer:

Explanation:

bracelets:

Example Question #5 : Calculating Ratio And Proportion

A box contains red and blue marbles.  The probablity of picking a red is .  There are 30 blue marbles.  How many total marbles are there?

Possible Answers:

Correct answer:

Explanation:

If  are red, then  are blue, and the number of blue marbles can be written as

Plug in the number of blue marbles, 30, and solve for the total marbles.

Example Question #6 : Calculating Ratio And Proportion

On a map, one and a half inches represents sixty actual miles. In terms of , what distance in actual miles is represented by  inches on the map?

Possible Answers:

Correct answer:

Explanation:

Let  be the number of actual miles. Then the proportion statement to be set up, with each ratio being number of actual miles to number of map inches, is:

Simplify the left expression and solve for 

Example Question #7 : Calculating Ratio And Proportion

The Kingdom of Zenda uses an unusual currency system. It takes 16 kronkheits to make a grotnik and 12 grotniks to make a gazoo. 

At current, $1 can be exchanged for 8 grotniks and 8 kronkheits. For how much American currency can a visitor from Zenda exchange a 100-gazoo bill, to the nearest cent? 

Possible Answers:

None of the other choices is the correct amount.

Correct answer:

Explanation:

$1 can be exchanged for 8 grotniks and 8 kronkheits, or, equivalently, 8.5 grotniks  (8 kronkheits is one-half of a grotnik). 100 gazoos is equal to  grotniks. Therefore, if  is the number of dollars that can be exchanged for the 100-gazoo bill, we can set up the proportion:

Solve for :

That is, the 100-gazoo bill can be exchanged for $141.18.

Example Question #8 : Calculating Ratio And Proportion

In a certain classroom all of the students are either sophomores or juniors. The number of boys and girls in the classroom are equal. Of the girls,  are sophomores, and there are 24 junior boys. If the number of junior boys in the classroom are in the same proportion to the total amount of boys as the number of sophomore girls are to the total number of girls, how many students are in the classroom?

Possible Answers:

Correct answer:

Explanation:

This question seems convoluted but is actually more simple than it seems. We are told that the number of girls and boys in the classroom are equal and that  of the girls are sophomores. We are then told that 24 of the boys are juniors, and that they represent a proportion of total boys equal to the proportion of sophomore girls to total girls. This means that:

 

  ==>       where  is the total number of boys.

If we know that the number of boys and girls in the class are equal, then the total number of students in the class = 112.

Example Question #9 : Calculating Ratio And Proportion

The Duchy of Grand Fenwick uses an unusual currency system. It takes 24 tiny fenwicks to make a big fenwick. 

At current exchange rates, 1 big fenwick can be exchanged for $3.26 American currency. For how much in Grand Fenwick currency can an American tourist exchange $300 (rounded to the nearest tiny fenwick)?

Possible Answers:

92 big fenwicks and 1 tiny fenwick

None of the other choices gives the correct amount of currency.

108 big fenwicks and 16 tiny fenwicks

40 big fenwicks and 18 tiny fenwicks

296 big fenwicks and 16 tiny fenwicks

Correct answer:

92 big fenwicks and 1 tiny fenwick

Explanation:

$3.26 can be exchanged for 1 big fenwick, or, equivalently, 24 tiny fenwicks. We can set up a proportion statement, where  is the number of tiny fenwicks for which $300 can be exchanged:

Solve for :

 

The answer is 2,209 tiny fenwicks, which can be counted up with division:

or 92 big fenwicks and 1 tiny fenwick.

Example Question #10 : Calculating Ratio And Proportion

Five different pizza places offer five different specials. Assuming that all of these pizzas are of the same thickness and that all are of the same quality, which of the following is the best buy?

Possible Answers:

A 12 inch by 8 inch rectangular pizza for $9.99

A round pizza 10 inches in diameter for $5.99

A 10 inch by 10 inch square pizza for $7.99

A 9 inch by 9 inch square pizza for $6.99

A round pizza 12 inches in diameter for $8.99

Correct answer:

A round pizza 10 inches in diameter for $5.99

Explanation:

Since all of the pizzas are of the same thickness and quality, to determine the best bargain, calculate the price per square inch of each. The least amount will mark the best bargain.

Edit this later

A round pizza 10 inches in diameter for $5.99:

The area of the pizza in square inches is   

The cost per square inch:   or 7.6 cents

 

A round pizza 12 inches in diameter for $8.99

The area of the pizza in square inches is 

The cost per square inch:   or 7.9 cents

 

A 9 inch by 9 inch square pizza for $6.99

The area of the pizza in square inches is 

The cost per square inch:   or 8.6 cents 

 

A 10 inch by 10 inch square pizza for $7.99

The area of the pizza in square inches is 

The cost per square inch:  or 8.0 cents

 

A 12 inch by 8 inch rectangular pizza for $9.99:

The area of the pizza in square inches is 

The cost per square inch:   or 10.4 cents

 

The round pizza 10 inches in diameter for $5.99 is the best buy.

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