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

Options

A. 23
B. 36
C. 38
D. 40

Explanation

Mean of first 13 observations = 32
`therefore " Sum of all first 13 observations" = (32 xx 13) = 416`
Mean of last 13 observations = 40
`therefore "Sum of all last 13 observations" = (40 xx 13) = 520`
Mean of 25 observations = 36
`therefore "Sum of all first 25 observations" = (36 xx 25) = 900`
Hence, 13th observation = `416+520-900 = 36`
Hence, (b) is the correct answer