Arithmetic mean of 9 observations was calculated as 45. In doing so an observation was wrongly
taken as 42 for 24. What would then be the correct mean?
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Mean of 9 observation =45.
xˉ=45
n=9
xˉ=n∑x
∑x=xˉn=45×9=405
Sum of all observation are 405.
Now an observation was wrongly taken as 42 for 24.
∴ 42−24=18 was mistakely added more.
∴ ∑x−18=387=∑y [the correct sum of all observation.]
∴yˉ=n∑y=9387=43
∴43 is the correct mean.
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