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Register now and save up to $200 Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Magoosh Study with Magoosh GMAT prep Available with Beat the GMAT members only code • Get 300+ Practice Questions 25 Video lessons and 6 Webinars for FREE Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code • 5-Day Free Trial 5-day free, full-access trial TTP Quant Available with Beat the GMAT members only code OG16 - PS 162 tagged by: Brent@GMATPrepNow This topic has 3 expert replies and 0 member replies amina.shaikh309 Senior | Next Rank: 100 Posts Joined 23 Apr 2016 Posted: 31 messages OG16 - PS 162 Thu May 26, 2016 5:56 am Elapsed Time: 00:00 • Lap #[LAPCOUNT] ([LAPTIME]) Need free GMAT or MBA advice from an expert? Register for Beat The GMAT now and post your question in these forums! GMAT/MBA Expert Brent@GMATPrepNow GMAT Instructor Joined 08 Dec 2008 Posted: 10757 messages Followed by: 1212 members Thanked: 5140 times GMAT Score: 770 Thu May 26, 2016 6:01 am Quote: 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 had ESTIMATED for the job, in hours? 28 24 16 14 12 Here's an algebraic solution: Let h = # of hours that Don ESTIMATED for the job. So, h + 4 = ACTUAL # of hours it took Don to complete the job. So, IF Don, had completed the job in h hours, his RATE would have =$336/h
However, since Don completed the job in h+4 hours, his RATE was actually = $336/(h + 4) ...consequently, he earned 2$ per hour less than his regular hourly rate.
In other words, (John's estimated rate) - 2 = (John's actual rate)
So, $336/h - 2 =$336/(h + 4)

ASIDE: since the above equation is a bit of a pain to solve, you might consider plugging in the answer choices to see which one works.

Okay, let's solve this: $336/h - 2 =$336/(h + 4)
To eliminate the fractions, multiply both sides by (h)(h+4) to get: 336(h+4) - 2(h)(h+4) = 336h
Expand: 336h + 1344 - 2h² - 8h = 336h
Simplify: -2h² - 8h + 1344 = 0
Multiply both sides by -1 to get: 2h² + 8h - 1344 = 0
Divide both sides by 2 to get: h² + 4h - 672 = 0
Factor (yeeesh!) to get: (h - 24)(h + 28) = 0
Solve to get: h = 24 or h = -28
Since h cannot be negative (in the real world), h must equal 24.

Cheers,
Brent

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Thu May 26, 2016 8:09 am
Quote:
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 had estimated for the job, in hours?

28
24
16
14
12
We can PLUG IN THE ANSWERS, which represent the estimated time: 28, 24, 16, 14, or 12.
The actual time was 4 hours longer: 32, 28, 20, 18, or 16.
Both the estimated time and the actual time must divide evenly into 336 (the labor cost).
Since 336 is not a multiple of 32, eliminate A.
Since 336 is not a multiple of 20, eliminate C.
336 is not a multiple of 9, since the sum of its digits is not a multiple of 9.
Thus, 336 is not a multiple of 18; eliminate D.

The correct answer must be B or E.

Answer choice B: estimated time = 24, actual time = 28
Estimated payrate = 336/24 = 14.
Actual payrate = 336/28 = 12.
Difference = 14-12 = 2.
Success!

Note that we had to try only ONE answer choice -- a very efficient way to solve the problem.

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Thu May 26, 2016 2:49 pm
If we've got

336 = x * y

and

336 = (x + 4) * (y - 2)

We could factor 336 to look for solutions. Since the answers are likely to have both the time and the hourly rate (in an attempt to trap us if we're not careful), we might cheat with them and assume that they multiply to our number ... which, of course, they do!

336 = 28 * 12
336 = 24 * 14

Since Don's estimate had a lower time and a higher hourly rate, his estimate must've been 24 * 14. We want the time, which must be LOWER than the time in the other equation, so our answer is 24.

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