The mean of 25 observations is 36. Out of these observations, the mean of first 13 is 32 and that of the last 13 is 40. The 13th observation is
Mean of 25 observations 36.
Sum of 25 observations = 25 × 36 = 900.
Mean of first 13 observations = 32
Sum of first 13 observations = 13 × 32 = 416.
Means of last 13 observations = 40
Sum of last 13 observations = 13 × 40 = 520.
Hence,
13th observation = (sum of first 13 observation + sum of last 13observations) – sum of 25 observations.
13th observation = 416 + 520 – 900 = 936 – 900 = 36
Hence, 13th observation = 36.