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Unofficial Guide 2016 PS 160

I’m going to do a number of these posts. You can think of them as commentary on the 2016 Official Guide for GMAT Review. I’m going to use the abbreviations PS, DS, RC, CR, and SC for Problems Solving, Data Sufficiency, Reading Comprehension, Critical Reasoning, and Sentence Correction. Sometimes I’ll present alternative solutions, more detailed solutions, and, occasionally an example problem.

I can’t reproduce the problem here, so if you don’t have your official guide handy, now would be the time to break it out – page 175

The suggested solution is a relatively simple equation, and in the solution the GMAC geniuses perform the following calculation

\(\Large\frac{207}{1.15}\)\( = 180\)

Obvious right? I mean, who can’t do that in their head? In fact, why do they give you a scratch pad in the first place?

I’m guessing you don’t like doing long division, so I suggest you check your answers. But where to start? Some say B, some D, and some insist on C. In general, I recommend checking B or D, as opposed to C, but there’s not such a difference that it’s worth worrying about.

In any case, as long as you can tell whether an answer is too large or too small, you should only have to check two to find the correct one.

In PS 160 B or D is the way to go, but not for methodological reasons – if you’re going to check your answers to avoid ugly calculations, CHECK NICE ANSWERS. Do you want to check $12.00 or $13.80, or, god forbid, $11.73? Definitely $12.00 or $14, and probably $12.00. I like 12. It’s a nice number. Lots of divisors. I really don’t like 7, so 14 and I don’t get along well.

Anyway:

\({12}\times{15} = 180\)

\({180}\times{1.15} = 180 + {180}\times{0.1} + {180}\times{0.05} = 180 + 18 + 9 = 207\)

Just in case that last part is confusing, here’s a breakdown: ten percent of 180 is 18 (divide by 10 or multiply by 1/10); five percent of 180 is half of ten percent (or 1/20th of 180): 9; fifteen percent of 180 is 10% + 5% = 18 + 9 = 27. Don’t you just love benchmark percents and fraction decimal equivalents.

180 + 27 = 207. The correct answer is B.