A contract is to be complete in 50 days and 105 men were set to work, each working 8 h a day. After 25 days, 2/5th of the work is finished. How many additional men be employed, so that the work may be completed on time, each man now working 9 h a day?

According to the formula
M₁D₁T₁/W₁= M₂D₂T₂/W₂
Given M₁ = 105 D₁ = 25 T₁ = 8 W₁ = 2/5
Now let the additional men be N
Then, M₂ = 105 + N, T₂ = 9, D₂ = 25 and W₂ =1 - (2/5) = 3/5
On putting these value in the above formula
(105 x 25 x 8) / (2/5) = [(105 + N) x 25 x 9] / (3/5)
⇒ (105 x 8) / 2 = (105 + N) x (9/3)
⇒ 105 x 4 = (105 + N) x 3
⇒ 105 x 4 = 105 x 3 +3N
⇒ 3N = 105
∴ N = 35 men