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

विकल्प

• 9

• 11

• 13

• 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

`(x+(x+2)+(x+4)+(x+6)+(x+8))/5`

`=(x+x+2+x+4+x+6+x+8)/5`

` =(5x+20)/5`

`=(5(x+4))/5`

= x+4

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

x+4 =11

⇒ x = 11 - 4

⇒ x= 7

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

`(7+9+11)/3`

`=27/3`

=9