Question

If the mean of the observations: x, x + 3, x + 5, x + 7, x + 10 is 9, the mean of the last three observations is ______.

Options

• `10 1/3`

• `10 2/3`

• `11 1/3`

• `11 2/3`

Answer 1

If the mean of the observations: x, x + 3, x + 5, x + 7, x + 10 is 9, the mean of the last three observations is `underlinebb(11 1/3)`.

Explanation:

Given that, the mean of the observations x, x + 3, x + 5, x + 7 and x + 10 is 9.

∴ `(x + x + 3 + x + 5 + x + 7 + x + 10)/5 = 9`

⇒ 5x + 25 = 45

⇒ 5x = 20

⇒ x = 4

∴ Last three observations are x + 5 = 4 + 5 = 9, x + 7 = 4 + 7 = 11

And x + 10 = 4 + 10 = 14

So, the mean of last three observations = `(9 + 11 + 14)/3 = 34/3 = 11 1/3`

Hence, the mean of last three observations is `11 1/3`.