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Question
Arithmetic mean of 15 observations was calculated as 85. In doing so an observation was wrongly taken as 73 for 28. What would be correct mean?
Solution
Arithmetic mean = `"Sum of all observations"/"Number of observations"`
85 = `"Sum of 15 observations"/15`
85 × 15 = sum of 15 observations
1275 = sum of 15 observations
Wrong observation = 73
Correct observation = 28
∴ Correct Mean = `"Sum − Wrong value + Correct value"/"Number of observations"`
= `(1275 - 73 + 28)/15`
= `(1202 + 28)/15`
= `1230/15`
= 82
Correct mean = 82
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