Correct Answer: 5

Solution: (5)

$\because 28$ men’s 1 day’s work $=\frac{1}{15}$

$\therefore 1$ man’s 1 day’s work $=\frac{1}{28 \times 15}$

$\therefore 20$ men’s 1 day’s work $=\frac{20}{28 \times 15}=\frac{1}{21}$

$\therefore 20$ men’s $\frac{42}{5}$ days’ work $=\frac{42}{5} \times \frac{1}{21}=\frac{2}{5}$

Remaining work $=1-\frac{2}{5}=\frac{3}{5}$

Now, 36 women do $\frac{3}{5}$ of the work in $\frac{42}{5}$ days.

$\therefore \frac{M_{1} D_{1}}{W_{1}}=\frac{M_{2} D_{2}}{W_{2}}$

$\Rightarrow \frac{36 \times 42}{\frac{3}{5} \times 5}=\frac{40 \times 7}{W_{2}}$

$\Rightarrow 12 \times 42 \times W_{2}=40 \times 7$

$\Rightarrow W_{2}=\frac{40 \times 7}{12 \times 42}=\frac{5}{9}$

$\therefore$ Remaining work $=1-\frac{5}{9}=\frac{4}{9}$