Eight painters can paint a school building in 15 days. How many days will 12 painters take, working at the same rate?

Explanation

1. 01

   More painters means fewer days, so this is inverse variation: painters × days stays constant.

2. 02

   $8 \times 15 = 120$ painter-days, so 12 painters need $120 \div 12 = 10$ days.