londonluddite wrote:
For each of her sales, a saleswoman receives a commission equal to 20 percent of the first $500 of the total amount of the sale, plus 30 percent of the total amount in excess of $500. If the total amount of one of her sales was $800, the saleswoman’s commission was approximately what percent of the total amount of the sale?
A. 22%
B. 24%
C. 25%
D. 27%
E. 28%
khan0210 wrote:
I have a question
Given that everyone has solved this,
if I do (19/80)*100 = 23.75% ~ 24%
Hence, choice B is the answer
if I round off 19 to 20 in order to get (20/80)*100=25%
Choice C is wrong.
So my question is, what is the way to ensure I am not falling into this rounding off calculation error?
Would you suggest not doing the rounding off. However, in other gmat questions rounding off is very helpful.
khan0210 , if answers are too close together, as here, do not estimate.
Determining what constitutes "too close together" is not an exact science.
But one and two
percent between answers?
\(\frac{1}{100}\) and \(\frac{2}{100}\)?
And hundreds of dollars at issue?
Don't round.
I agree that to estimate or round is often a shrewd strategy.
Experience with a lot of questions is the best teacher. I can say safely, however, that when the difference between and among answers is 1-2%, you should not estimate. See
Bunuel above. mikemcgarry wrote an excellent overview on the matter, titled
The Power of Estimation on GMAT Quant, here.Hope that helps.
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