24 men working at 8 hours per day can do a piece of work in 15 days. In how many days can 20 men working at 9 hours per day do the same work?

Explanation: Let \(M\) be the number of men, \(H\) be the hours per day, and \(D\) be the number of days. The total work units are constant: \(M_1 \times H_1 \times D_1 = M_2 \times H_2 \times D_2\). Given: \(M_1 = 24\), \(H_1 = 8\), \(D_1 = 15\). Total Work Units = \(24 \times 8 \times 15 = 2880\). Required: \(M_2 = 20\), \(H_2 = 9\), \(D_2 = ?\). \(2880 = 20 \times 9 \times D_2\). \(2880 = 180 \times D_2\). \(D_2 = \frac{2880}{180} = \frac{288}{18}\). \(D_2 = 16\) days.