Question

The mean of 15 observation is 28 if the mean of first 8 observation is 25 and that of the last 8 is 30 find the 8th onservation

Answer 1

$since \: the \: mean \: of \: 15 \: observation \: = 28 \\ mean \: of \: 15 \: obseration \: = 15 \times 28 = 420 \: \\ mean \: of \: 8 \: observation \: = 25 \times 8 = 200 \: \\ mean \: of \: last \: 8 \: observtion = 30 \times 8 = 240 \\ mean \: of \: 8 \: observtion = 240 + 200 - 420 = 0$
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