GMAT Math

Can anybody explain the difference of logic behind in Question Nos. 59 and 70 in the Official Quant Guide?

Q 59 asks for the value of "exactly 2 standard deviation less than mean" and calculates it as: " [mean - 2 standard devistion]", while Q 70 asks for "value more than 2.5 standard deviation from the mean" and calculates it as in the range: "[mean - 2.5 standard devistion] and [mean + 2.5 standard devistion]. Why the range in Q 70 not in Q 59?

Nauman

snuman wrote:Can anybody explain the difference of logic behind in Question Nos. 59 and 70 in the Official Quant Guide?

Q 59 asks for the value of "exactly 2 standard deviation less than mean" and calculates it as: " [mean - 2 standard devistion]", while Q 70 asks for "value more than 2.5 standard deviation from the mean" and calculates it as in the range: "[mean - 2.5 standard devistion] and [mean + 2.5 standard devistion]. Why the range in Q 70 not in Q 59?

Nauman

Hey,

The main thing to notice in the question is that 59 is explicitly asking for a number by saying "exactly 2" deviations less than the mean.

In 70, saying "a value more than 2.5 deviations away from the mean", is different from saying "2.5 deviations more than the mean." (Notice the difference in word order)

Think of it like a number line:
1. the first one is like asking for a numbers that are 2 units away from zero {-2,2}

2. the second one is asking for a number 2 units more than 0 or 2.

Hope that help explain the difference in what they are asking. Again, it is mostly a difference in the wording of the question. Let me know if you have any more questions.

I appreciate your reply. But im still confused.

You come up with "2" for a value two units more than zero on a number line, but the question No. 70 calculates it differently and instead of a single value, it goes for range.

Hi Mpalmer22,

I got it now. Actually i got confused with your point 1 and 2. But i think you have made it clear by highlighting the difference in wordings.

Thanks

Nauman