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Source: Official Guide for the GMAT 13th Ed. Problem Solving; #137 Official Guide for the GMAT 2015 14th Ed. Problem Solving; #137


At his regular hourly rate, Don had

At his regular hourly rate, Don had estimated the labor cost of a repair job as $336 and he was paid that amount. However, the job took 4 hours longer than he had estimated and, consequently, he earned $2 per hour less than his regular hourly rate. What was the time Don estimated for the job, in hours?

2 Explanations


Sam Kinsman

Hi Diego,

Yes, there is another way to do this. Once you get to 4r - 2t - 8 = 0, divide both sides by 2, then solve for t.

4r - 2t - 8 = 0
2r - t - 4 = 0
2r - 4 = t

Now, we can test each answer choice by plugging in. The questions asks us to find the hours that the job was estimated to take, so we are being asked for t.

So plug in the possible values of t, and use (2r - 4 = t) to find the value of r. Then, we can multiply r*t, and the result must give us 336 (because we know that rt = 336). If the result you get is 336, that's the right answer. If not, eliminate that one and move on to another answer choice.

Answer choice (B) is 24. When we plug in 24, we get:

2r - 4 = t
2r - 4 = 24
2r = 28
r = 14

r * t = 14 * 24 = 336

So (B) is correct!

Feb 23, 2017 • Comment


Gravatar Mike McGarry, Magoosh Tutor

Dec 28, 2013 • Comment


Is there any other way to solve the problem ?

Feb 22, 2017 • Reply

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