The mean of first 8 observations is 18 and last 8 observations is 20 . If the mean of all 15 observations is 19 , find the 8 th observation?
The mean of first 8 observation = 18
So, Sum of first 8 observation = 818 = 144
And, the mean of last 8 observation = 20
So, sum of last 8 observation = 820 =160
Sum of 16 observation = 144 +160 = 304
Sum of 15 observation = (1519) =285
Eighth observation = (sum of 16 observation) – (sum of 15 observation)
= (304) – (285) = 19
Hence, 8th observation is 19.