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, 8^{th} observation is 19.

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