The mean value of 20 observations was found to be 75, but later on it was detect

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Question

The mean value of 20 observations was found to be 75, but later on it was detected that 97 was misread as 79. Find the correct mean.

Options:

A . 75.8

B . 75.7

C . 75.6

D . 75.9

Answer: Option D
Answer: (d)Difference = 97 – 79 = 18 True average = 75 + $18/20$ = 75.9 Aliter : Using Rule 26, If average of n numbers is m later on it was found that a number 'a’ was misread as 'b’. The correct average will be = m +${\text"(a-b)"}/ \text"n"$. Here, n = 20, m = 75 a = 97, b = 79 Correct mean = m + ${\text"(a - b)"}/\text"n"$= 75 +${(97 -79)}/20$= 75 +$18/20$= 75 + 0.9 = 75.9

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