16 boys or 12 women can do a piece of work in 28 days. In how many days will the same work be done by 4 boys and 4 women, if they all work together?

16 boys or 12 women can do a piece of work in 28 days.

16 boys $$\times$$ 28 = 12 women $$\times$$ 28

16 boys = 12 women

4 boys = 3 women    Eq.(i)

4 boys and 4 women can do the same work in 'y' days.

12 women $$\times$$ 28 = (4 boys + 4 women) $$\times$$ y

Put Eq.(i) in the above equation.

12 women $$\times$$ 28 = (3 women + 4 women) $$\times$$ y

12 women $$\times$$ 28 = 7 women $$\times$$ y

$$12\times\ 28\ =7\times y$$

$$12\times\ 4\ =y$$

y = 48

So 4 boys and 4 women can do the same work in 48 days.