90 men are engaged to do piece of work in 40 days but it is found that in 25 days, 2/3 work is complete. How many men should be allowed to go off, so that the work finished in time?

Let N men are allowed to go off,
M₁= 90, D₁ = 25, D₂ = 15
W₁ = 2/3, W₂ = 1 - (2/3) = 1/3
M₂ = 90 - N
According to the formula, M₁D₁W₂ = M₂D₂W₁
⇒ (90 x 25) (1/3) = (90 - N) x 15 x (2/3)
⇒ 90 x 25 x (1/3) = 10(90 - N)
⇒ 75 = 90 - N
∴ N = 90 - 75 = 15