GMAT Math : Calculating ratio and proportion

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #11 : Ratio & Proportions

A fathom is a unit of underwater depth equal to six feet. 

Express two miles in fathoms.

Possible Answers:

Correct answer:

Explanation:

Multiply 2 miles by 5,280 feet per mile, then divide by 6 feet per fathom:

Example Question #12 : Ratio & Proportions

A furlong is a measure of length used in horse racing. Eight furlongs are equal to one mile.

Express 20 furlongs in feet.

Possible Answers:

Correct answer:

Explanation:

Divide 20 furlongs by 8 furlongs per mile, then multiply by 5,280 feet per mile.

Example Question #13 : Ratio & Proportions

127 people signed up for a subscription service. 45 signed up for weekly deliveries, 34 for monthly deliveries, and the rest for annual deliveries. What is the ratio of weekly subscribers to annual subscribers?

Possible Answers:

Correct answer:

Explanation:

Let's first find the number of annual subscribers:

The ratio of weekly subscribers to annual subscribers is therefore .

Example Question #11 : Ratio & Proportions

A clothing store is having a sales for the holiday season. They mark down all items by . What is the sales price of a suit whose original price is ?

Possible Answers:

Correct answer:

Explanation:

We start by finding the value of the mark down:

Therefore, the mark down is 43.8% or 0.438, which means that the new price of the suit is:

Example Question #15 : Ratio & Proportions

Noah and Lilly both work for Company ABC. Lilly earns  more than Noah, and each year every employee gets a  salary increase. In 2012, Noah's salary was .

What was Lilly's salary in 2013?

Possible Answers:

Correct answer:

Explanation:

We start by finding Lilly's salary in 2012:

$60,000 x 1.20 = $60,000 + $12,000 = $72,000

Then we account for the annual 10% increase to find Lilly's salary in 2013:

$72,000 x 1.10 = $72,000 + $7,200 = $79,200

So Lilly's salary in 2013 was $79,200.

Example Question #11 : Ratio & Proportions

Company sells  liters of soda for , and Company sells  liters of soda for .

If the amount of soda sold per dollar is the same for each company, what is ?

Possible Answers:

Correct answer:

Explanation:

Since the amount of soda per dollar is the same for each company, we can equate the 2 ratios

And solve

(Cross multiply)

Example Question #12 : Ratio & Proportions

Ms. Lopez earned $236.25 after working 15 hours last week. At this rate, how much will she have earned if she works 25 hours?

Possible Answers:

Correct answer:

Explanation:

The first thing we must do is set up our equation. We do this by writing our earnings to hours worked ratio:

where  represents her earnings after working 25 hours.

We can then solve this equation for .

Then, 

Example Question #11 : Ratio & Proportions

George just finished the first week of his new job. He calculated that if he works 50 hours in two weeks, his biweekly paycheck will be $812.50. If he has worked a total of 27 hours so far, how much additional money must he earn in order to reach $812.50? 

Possible Answers:

$621.00

$432.75

$373.75

$438.75

Correct answer:

$373.75

Explanation:

He has worked 27 hours out of the 50 hours calculated. As such, we are asked how much he will earn after working the remaining 23 hours. 

We can first find his hourly pay and then calculate his earnings for 23 hours.

where  represents his hourly earnings

He earns $16.25 an hour

We can now calculate how much he earns for the remaining 23 hours:

So, George needs $373.75. 

Example Question #1 : Proportion / Ratio / Rate

A small company's workforce consists of store employees, store managers, and corporate managers in the ratio 10:3:1. How many employees are either corporate managers or store managers if the company has a total of  employees?

Possible Answers:

Correct answer:

Explanation:

Let  be the number of store employees,  the number of store managers, and  the number of corporate managers.

, so the number of store employees is .

, so the number of store managers is .

, so the number of corporate managers is .

Therefore, the number of employees who are either store managers or corporate managers is .

Example Question #13 : Ratio & Proportions

A scale model of the newest Mars rover has a wheel radius of  and its antennae are each  long. If the radius of the wheel on the actual rover is , what is the length of the antennae on the actual rover?

Possible Answers:

Correct answer:

Explanation:

Setting up a proportion here is the way to go. To make our proportion even easier to solve, set it up in such a way that your unknown (antennae length for the actual rover) is in the numerator. Recall that in a proportion, we want to have similar parts together. In this case, we will keep the wheel radii on the left and the antennae lengths on the right.

By leaving our unknown on top, we can solve this in one fell swoop. Simply multiply both sides by  and simplify to get the answer.

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