Rate Problems


Work Rate ProblemsCarefully go through the following question types. These are the standard work rate problems that you would encounter in your GMAT Exam.

Working Together

In questions where individuals work at different speeds, we typically need to add their separate rates together. Make sure you keep your units straight. This doesn’t mean wasting time and writing each and every one out, but rather simply recognizing their existence. Note that when working together, the total time to complete the same task will be less than BOTH of the individual rates, but not necessarily in proportion. Nor, are you averaging or adding the given times taken. You must add rates.

Q) A worker can load 1 full truck in 6 hours. A second worker can load the same truck in 7 hours. If both workers load one truck simultaneously while maintaining their constant rates, approximately how long, in hours, will it take them to fill 1 truck?

A. 0.15
B. 0.31
C. 2.47
D. 3.23
E. 3.25

The rate of worker #1 is 1 truck/6 hours. This can also be 1/6 trucks/1 hour. The rate of worker #2 is 1/7. When together, they will complete 1/6 + 1/...


X and Y, two computer engineers, built identical websites at different constant rates. X, working alone for 7 hours, built some of the website; then Y, working alone for 6 hours, built the rest of the website. How many hours would it have taken X, working alone, to build all of the website?

1. X built one part 15 minutes
2. X built four times as many parts in 7 hours as Y built in 6 hours

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer

Statement 2 provides us with an equation relating the two rates: 7X = 4(6Y).

We can simplify this formula to get one rate in terms of the other. The first step is to calculate the expression on the right-hand side: 7X = 24Y.

Now divide both sides by 24: 7/24 X=Y.

Statement 2 is sufficient on its own.

Correct Answer B