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?

Answer 1

Here, mean = 80, number of observations = 50

∴ The sum of all observations = Mean x 

Total number of observations 

∴ The sum of 50 observations = 80 x 50 = 4000 

One of the observation was 19. 

However, by mistake it was recorded as 91. 

Sum of observations after correction = sum of 50 observation + correct observation – incorrect observation 

= 4000 + 19 – 91 = 3928 

∴ Corrected mean

= 78.56 

∴ The corrected mean is 78.56.