Question

The means of 35 exhibition in 20 out of which means of first 18 observation is 15 and means of last 18 observation is 25 find the 18th observation

Answer 1

Mean = sum of observations / number of observations
20=sum/35
Sum= 35*20
Sum=700


Mean of first 18 observations = 15
15= sum of observations/ number of observations
15= sum/18
Sum = 18*15
= 270

Sum of last 18 observations =25
18= sum/25
Sum = 25*18
Sum=450

Value of 18 th observation = (450+270)-700. [ because 18th observation is getting added in both sums]
= 720-700
=. 20

Therefore, value of 18 th observation is 20