Choose the correct answer. Consider the first 10 positive integer… - Vidyadip

MCQ

Choose the correct answer. Consider the first 10 positive integers. If we multiply each number by -1 and then add 1 to each number, the variance of the numbers so obtained is:

✓
8.25
B
6.5
C
3.87
D
2.87

✓

Answer

Correct option: A.

8.25

Since, the first 10 positive integers are 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10.
On multiplying each number by -1, we get -1, -2, -3, -4, -5, -6, -7, -8, -9, -10 On adding 1 in each number.
We get 0, -1, -2, -3, -4, -5, -6, -7, -8, -9.
$\therefore\ \sum\text{x}_\text{i}=-\frac{9\times10}{2}=-45$
and $\sum\text{x}^2_\text{i}=0^2+(-1)^2+(-2)^2+\ ....\ +(9)^2=\frac{9\times10\times19}{6}=285$
$\text{SD}=\sqrt{\frac{285}{10}-\Big(\frac{-45}{10}\Big)^2}=\sqrt{\frac{285}{10}-\frac{2025}{100}}$
$=\sqrt{\frac{2850-2025}{100}}=\sqrt{8.25}$
Now, $\text{variance}=(\text{SD})^2=\big(\sqrt{8.25}\big)^2=8.25$

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