18 men can finish a piece of work in 20 days working 5 hours per day. In how many days a group of 12 men will finish twice the work when they are working 4 hours per day if 5 men of the first group are equal to 2 men of the second group?

30

5M₁ = 2M₂

Efficiency ratio = M₁ : M₂ = 2 : 5

⇒ Efficiency × Days = Total work

⇒ \(\frac{M_1\;×\;D_1\;×\;H_1\;×\;E_1}{E_2\;×\;D_2\;×\;H_2\;×\;E_2}\) = \(\frac{W_1}{W_2}\)

ATQ,

⇒ \(\frac{18\;×\;20\;×\;5\;×\;2}{12\;×\;D_2\;×\;4\;×\;5}\) = \(\frac{1}{2}\)

⇒ D₂ = 30 days