Question

The arthematic mean of 10 members is 7. the arthematic men of 15 members is 12 ,then the mean of all observations is?

Answer 1

Meet of all observations
$\frac{10 \times 7 + 15 \times 12}{10 + 15} = 10$

Answer 2

Sum of 10 members = 10 x 7 = 70

sum of 15 members = 15 x 12 = 180

Sum of 25 members = 180 + 70 = 250

Mean of all observation = 250/25 = 10

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