Mean = The sum of all observations/Total number of observations
∴ The sum of all observations = Mean x
Total number of observations
The mean of 5 observations is 50
Sum of 5 observations = 50 x 5 = 250 …(i)
One observation was removed and mean of remaining data is 45.
Total number of observations after removing one observation = 5 – 1 = 4
Now, mean of 4 observations is 45.
∴ Sum of 4 observations = 45 x 4 = 180 …(ii)
∴ Observation which was removed = Sum of 5 observations – Sum of 4 observations
= 250 – 180 … [From (i) and (ii)] = 70
∴ The observation which was removed is 70.