Help,

The mean of 25 observatios is 36. Out of thes,if the mean of first 13 observation is 32 and that of last 13 observation is 40,find the 13th observation.

Sum of 26 observation = 13 * 32 + 13 * 40 = 416 +520 = 936

Sum of 25 observation = (25 * 36) =900

Thirteenth observation = (sum of 26 observation) – (sum of 25 observation)

= (936) – (900) = 36

Hence, 13^{th} observation is 36.

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