20 men complete one-third of a work in 20 days. How many more men should be employed to finish the rest of the work in 25 more days?

Work done = 1/3
Remaining work = 1 - (1/3) = 2/3
Let the number of more men to be employed be N.
More work, More men (Direct proportion)
More days, Less men (Indirect proportion)
Work 1/3 : 2/3
Days 25 : 20
∴ 1/3 x 25 x (20 + N) = 2/3 x 20 x 20
⇒ (20 + N) = 800/25 = 32
∴ N = 32 - 20 = 12