The mean of 50 observations was 36. It was found later that

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The mean of 50 observations was 36. It was found later that an observation 48 was wrongly taken as 23. The corrected (new) mean is

The mean of 50 observations = 36
⇒ The sum of 50 observations = 50 × 36 = 1800

The correct mean =	1800 - 23 + 48
	50

=	1825	= 36.5
	50

Second method to solve this question with the help of given formula :
Here, n = 50, m = 36 , a = 48, b = 23

Correct Average = m +	(a -b)
	n

Correct Average = 36 +	(48 - 23)
	50

Correct Average = 36 +	25	= 36.5
	50