Can anyone please help me with the solution of this question? as I am getting different answers from what I am seeing in the 5LB. Book solution.

What do you think the answer is, and what’s the book saying?

Assuming that you’re using the first edition of the 5lb book, it’s an error from their side, and they’ve confirmed it. See Errata - 5 lb. Book, 1st Edition - GRE

In other words, 18.2 is the correct answer.

Thanks bro!!!

OK, and …?

Basically, if we want to calculate standard deviation the formula is 1st one, exception is for when it’s sample standard deviation then it would be 2nd formula.