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Question
The mean of 200 observations is 20. It is found that the value of 180 is wrongly copied as 280. Find the actual mean.
Solution
Since mean of 200 observations = 20
⇒ Sum of 200 observations
= 200 x 20
= 4000
⇒ Incorrect sum = 4000
∴ Correct sum
= Incorrect sum - Incorrect value + Correct value
= 4000 - 280 + 180
= 3900
∴ Correct mean
= `"Correct sum"/"Total number of observations"`
= `(3900)/(200)`
= 19.5.
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