Question

The number of cars sold in 5 consecutive days are given as 11, 12, 10, 8, 9. Find it's standard deviation using mean method.

• A. 1.41
• B. 3.23
• C. 5.26
• D. 6.45

Answer 1

The correct option is A 1.41

Arranging the numbers in ascending order, we get, 8, 9,10, 11,12.

Mean
$=\overline{x}=\frac{8+9+10+11+12}{5}=\frac{50}{5}=10$

$\begin{array}{ccc}xi& di=xi-\overline{x}& d{i}^2\\ & =xi-10& \\ 8& -2& 4\\ 9& -1& 1\\ 10& 0& 0\\ 11& 1& 1\\ 12& 2& 4\\ & & 10\end{array}$

Standard Deviation

$\sigma =\sqrt{\frac{\sum d{i}^2}{n}}$

$=\sqrt{\frac{10}{5}}$

$=\sqrt{2}\simeq 1.41$