Explanation

(b)
The formula for combined mean is
$\overline{X} = \frac{n_{1}{\overline{X}}_{1} + n_{2}{\overline{X}}_{2}}{n_{1} + n_{2}}$
We are given $\overline{X} = 25,\ {\overline{X}}_{1} = 26,\ {\overline{X}}_{2} = 21$. Let $n_{1} + n_{2} = 100$
and $n_{1}$ denotes men and $n_{2}$ denotes women
$n_{2} = 100 - n_{1}$
$\therefore 25 = \frac{26n_{1} + 21(100 - n_{1})}{100}\ \ \Rightarrow \ \ n_{1} = 80$
So, $n_{2} = 20$
Hence, the percentage of men and women is 80 and 20 respectively