What is the population standard deviation for the numbers: 75, 83, 96, 100, 121 and 125?  Pick one
A) 18.2  B) 20  C) 25  D) 26  E) 28

Rationale: 1 . firstly find the mean : mean = ( 75 + 83 + 96 + 100 + 121 + 125 ) ÷ 6 = 600 ÷ 6 = 100 2 . next find the variance . to calculate the variance , take each difference , square it , and then average the result : ( 75 - 100 ) 2 + ( 83 - 100 ) 2 + ( 96 - 100 ) 2 + ( 100 - 100 ) 2 + ( 121 - 100 ) 2 + ( 125 - 100 ) 2 = ( - 25 ) 2 + ( - 17 ) 2 + ( - 4 ) 2 + ( 0 ) 2 + ( 21 ) 2 + ( 25 ) 2 = 625 + 289 + 16 + 0 + 441 + 625 = 1996 so the variance = 1996 ÷ 6 = 332.66 . . . 3 . the standard deviation is just the square root of the variance = √ ( 332.66 . . . ) = 18.2 correct to 1 decimal places answer is a
Answer: A