Question

If mean of 10 observations is 20 and that of another 15 observations is 16. Find the mean of 25 observations

Answer 1

n1 = 10
X1 = 20

n2 = 15
X2 = 16

so, mean of total 25 observations will be ..

$x = \frac{n1 \times x1 \: \: + \: n2 \times x2}{n1 + n2}$
$= > x = \frac{(10 \times 20) + (15 \times 16)}{10 + 15} = \frac{440}{25} = 17.6$
so, required mean = 17.6