20 boys do one fourth of work in 25 days. How many more boys will be required to complete the remaining work in 50 days?

Using, $$\frac{M_1D_1}{W_1}$$ $$=\frac{M_2D_2}{W_2}$$, where $$M$$ is number of men, $$D$$ is number of days and $$W$$ is work done.

Let total work to be done = $$4$$ units

=> Remaining work = $$4-\frac{1}{4}\times4=3$$ units

Let $$x$$ more boys are required.

=> $$\frac{20\times25}{1}=\frac{(x+20)\times50}{3}$$

=> $$\frac{(x+20)}{3}=\frac{20\times25}{50}$$

=> $$x+20=10\times3=30$$

=> $$x=30-20=10$$

$$\therefore$$ 10 more boys will be required to complete the remaining work in 50 days.

=> Ans - (B)