If the average of 8 observations is 16 and the average of 4 observations is 64, then the average of (8 + 4 ) = 12 observations is-

Explanation

∵ The average of 8 observations = 16 ∴ The sum of 8 observations = 8 × 16 = 128 ∵ The average of 4 observations = 64 ∴ The sum of 4 observations = 4 × 64 = 256 ∴ The required average of (8 + 4) = 12 observations = $\frac{128 + 256}{12}$ = $\frac{384}{12}$ = 32 Therefore, option (c) is the correct answer.