$$\begin{gathered} \mathrm{Let} {\mathrm{x}}_{\mathrm{i}}\left(1 \le \mathrm{i} \le 10\right) \mathrm{be} \mathrm{ten} \mathrm{observation} \mathrm{of} \mathrm{a} \mathrm{random} \mathrm{variable} \mathrm{X}. \mathrm{If} \sum _{\mathrm{i} = 1}^{10}\left({\mathrm{x}}_{\mathrm{i}} - \mathrm{p}\right) = 3 \\ \mathrm{and} \sum _{\mathrm{i} = 1}^{10}{\left({\mathrm{x}}_{\mathrm{i}} - \mathrm{p}\right)}^2 = 9 \mathrm{where} 0 \ne \mathrm{p} \in \mathrm{R}, \mathrm{then} \mathrm{the} \mathrm{standard} \mathrm{deviation} \mathrm{of} \mathrm{these} \mathrm{observations} \mathrm{is} \end{gathered}$$

• $\frac{4}{5}$

• $\sqrt{\frac{3}{5}}$

• $\frac{9}{10}$

• $\frac{7}{10}$

The mean and variance of 8 observations are 10 and 13.5 respectively. If 6 of these observations are 5, 7, 10, 12, 14, 15, then the absolute difference of the remaining two observations is :

• 9

• 5

• 3

• 7

If the variance of the following frequency distribution :

Class :      10-20 20-30 30-40

Frequency : 2        x        2

is 50, then x is equal to ....

44.

If the mean and the standard deviation of the data 3, 5, 7, a, b are 5 and 2 respectively, then a and b are the roots of the equation : 

• x² - 20x + 18 = 0

• 2x² - 20x + 19 = 0

• x² - 10x + 19 = 0

• x² - 10x + 18 = 0