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Question
The calculated mean of 50 observations was 80. It was later discovered that observation 19 was recorded by mistake as 91. What was the correct mean?
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Solution
Mean = `"The sum of all observations"/"Total number of observations"`
∴ The sum of all observations = Mean x Total number of observations
∴ The sum of 50 observations = 80 x 50
= 4000
Sum of observations after correction = 4000 + 19 – 91
= 3928
∴ Corrected mean = `"Sum of observations after correction"/"Total number of observations"`
= `3928/50`
= 78.56
∴ The corrected mean is 78.56.
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