GMATD11 wrote:

70) if a certain sample of data has a mean of 20.0 and a standard deviation of 3.0,which of the following values is more than 2.5 standard deviation from the mean?

a) 12.0

b) 13.5

c) 17.0

d) 23.5

e) 26.5

the value must be more than 2.5 standard deviation above the mean or below the mean.so the range of values will be

20+7.5 = 27.5

20-7.5 = 12.5

I don't what to do next!!!!!!!!!

You've done all the work.

The answer is (a).

2.5 standard deviations is 7.5, as you've correctly calculated. So you need to find which value is further from 20 than 7.5

If you subtract 12 from 20, you get 8.

8 is more than 7.5

To put it another way, you've calculated the range of values within 2.5 standard deviations as 12.5 through 27.5

You're looking for a value that is outside that range.