# 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, 13th observation is 36.

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TOTAL SUM = 25 * 36 = 900

SUM OF FIRST 13 OBSERVATION ( FIRST 12 + 13TH ) = 13 * 32 = 416

SUM OF LAST 13 OBSERVATION ( 13TH + LAST 12 ) = 13 * 40 = 520

TOTAL SUM + 13 TH = 936

13TH OBSERVATION = 936 - 900 = 36

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