CA Foundation · Quantitative Aptitude · Measures of Central Tendency and Dispersion
For 10 observations, Σx = 50 and Σx² = 340. What is the standard deviation?
The standard deviation is 3. The mean of squares is 34 and the square of the mean is 25, so the variance is 9, and its square root is 3. Giving 9 would confuse variance with standard deviation.
- A3Correct
- B6.8
- C9
- D34
Explanation
Variance = Σx²/n − (Σx/n)² = 34 − 25 = 9, so SD = 3. The option 6.8 comes from forgetting to subtract the squared mean and wrongly taking a root-like figure; 9 is the variance and 34 is the mean of squares.
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