Question

If the mean of five observations x, x+2, x+4, x+6, x+8, is 11, then the mean of first three observations is

(a) 9

(b) 11

(c) 13

(d) none of these

Answer 1

The given data is x, x + 2, x + 4, x + 6 and x + 8. They are 5 in numbers.

The mean is

But, it is given that the mean is 11. Hence, we have

Then the first three observations are 7, 7 + 2, 7+4, that is, 7, 9, 11. Their mean is

Hence, the correct choice is (a).