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

Given, M₁ = 20.
M₂ = 20 + k
W₁ = 1/3, W₂ = 1 - 1/3 = 2/3
D₁ = 20 and D₂ = 25
According to the formula,
M₁D₁W₂ = M₂D₂W₁
⇒ 20 x 20 x (2/3) = (20 + k) x 25 x 1/3
⇒ 20 x 20 x (2/3) = (20 + k) x 25/3
⇒ 16 x 2 = 20 + k
∴ k = 32 - 20 = 12