# What will be the Last Three Mean Observation? If

If the mean of 5 observations x, x+2, x+4, x+6 and x+8 is 11, then the mean of last three observations is:

- 11
- 13
- 15
- 17

**Answer: (2) 13**

**Explanation:-**

**Given-**

5 observations are X, X + 2, X + 4, X + 6 and X + 8.

Mean = 11

Formula-

Mean of the observation = Sum of the observation /number of the observation

Then, (X + X + 2 + X + 4 + X + 6 + X + 8)/5 = 11

5 X + 20 = 11 x 5

5 X = 55- 20

5 X = 35

X = 35/5

X = 7

Now, the value of the last three observations X + 4 = 7 + 4 = 11, X + 6 = 7 + 6 = 13 & X + 8 = 7 + 8 = 15

Then, the mean of the last three observations = (11 + 13 + 15)/3

= 39/3

= 13

Hence, the answer is (2) 13.