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