10 workers, working 6 hours a day, dig a 60 m long drainage trench in 12 days. How many days will 15 workers, working 8 hours a day, take to dig a 90 m trench of the same width and depth?

Explanation

1. 01

   Use $\frac{M_1D_1H_1}{W_1} = \frac{M_2D_2H_2}{W_2}$.

2. 02

   $\frac{10 \times 12 \times 6}{60} = \frac{15 \times D \times 8}{90}$, so $12 = \frac{120D}{90}$.

3. 03

   $D = \frac{12 \times 90}{120} = 9$ days.