Question

If the algebraic sum of deviations of 20 observations from 30 is 20, then the mean of observations is

• A. 30
• B. 30.1
• C. 29
• D. 31

Answer 1

Answer: (D)

31

Answer 2

$\sum_{i = 1}^{20}{(x_{i} - 30) = 20}$ ⇒ $\sum_{i = 1}^{20}{x_{i} - 20 \times 30 = 20}$

⇒ $\sum_{i = 1}^{20}{x_{i} = 620}$. Mean = $\frac{\sum_{i = 1}^{20}x_{i}}{20} = \frac{620}{20} = 31$.