Question

The mean of 25 observations 36.Out of these observations,the mean of first 13 observations is 32 and that of the last 13 observations is 40.Find the 13th observation.

Answer 1

Mean of 25 observations = 36

Sum of observations = 36 × 25 = 900

Mean of first 13 observations = 32

Sum of first 13 observations = 32 × 13 = 416

Mean of last 13 observations = 40

Sum of last 13 observations = 40 × 13 = 520

∴13^th observation = (Sum of first 13 observations + Sum of last 13 observations) – Sum of all observations

= (416 + 520) – 900

= 936 – 900

= 36