Let the total work be 3 units and additional men employed after 18 days be ‘x’.
=> Work done in first 18 days by 20 men working 8 hours a day = (1/3) x 3 = 1 unit
=> Work done in last 10 days by (20 + x) men working 9 hours a day = (2/3) x 3 = 2 unit
Here, we need to apply the formula M1 D1 H1 E1 / W1 = M2 D2 H2 E2 / W2, where
M1 = 20 men
D1 = 18 days
H1 = 8 hours/day
W1 = 1 unit
E1 = E2 = Efficiency of each man
M2 = (20 + x) men
D2 = 10 days
H2 = 9 hours/day
W2 = 2 unit
So, we have
20 x 18 x 8 / 1 = (20 + x) x 10 x 9 / 2
=> x + 20 = 64
=> x = 44
Therefore, additional men employed = 44
