**Problem of the day: June 29, 2021**

In the **Quant concept** part of the problem of the day, the data question asks to find standard deviation of data:

(75,81)

I understand the mean is 75 and therefore the data are separated at 3 units from the mean, meaning the individual difference is: -3 and +3.

Greg says the the standard deviation is therfore 3.

However, if I use the formula that I have been taught in school, the formula is:

s.d. = \sqrt{\frac{\sigma{d^2}}{n-1}}

Using this formula, I get the answer 3*\sqrt{2}

The problem here seems to be between the assumptions and formula to be used.

Which is the correct formula that GRE prescribes to?

In the case you have mentioned, we have the entire dataset = [75, 81], we therefore use the population formula