Given, women = $\frac{1}{3}$

Men = $1-\frac{1}{3}=\frac{3-1}{3}=\frac{2}{3}$

Married women = $\frac{1}{3}of\frac{1}{2}=\frac{1}{6}$ of whole office is married women.

Married women who have children = $\frac{1}{6}of\frac{1}{3}=\frac{1}{18}$ 

Married men= $\frac{2}{3}of\frac{3}{4}=\frac{1}{2}$ of whole workers

Married men who have children = $\frac{1}{2}of\frac{2}{3}=\frac{1}{3}$ of married men. 

Married workers who have children = $\left(\frac{1}{18}+\frac{1}{3}\right)=\frac{1+6}{18}=\frac{7}{18}$ Part of whole workers

$\left(1-\frac{7}{18}\right)=\frac{18-7}{18}=\frac{11}{18}$ Worker does not have children. ans.

Balance = 20,00,000

To wife = (2/5)*20,00,000 = 8,00,000

Remain =20,00,000-8,00,000=12,00,000

To son = (¼)*12,00,000 = 3,00,000

Remain 12,00,00-3,00,000 = 9,00,000

Donated = (2/9)* 9,00,000 = 2,00,000 (Ans.)

$\frac{1}{2}\times \frac{1}{4}\times \frac{1}{8} = \frac{1\times 1\times 1}{2\times 4\times 8}=\frac{1}{64}$

$\frac{১}{৩}+\frac{২}{৭}-\frac{১}{২১}$

$=\frac{৭+৬-১}{২১}=\frac{১২}{২১}=\frac{৪}{৭}$