A fast horse travels 240 Li a day, and a slow horse 150 Li a day. The slow horse goes 12 days first. How many days can the fast horse catch up with the slow horse?

A fast horse travels 240 Li a day, and a slow horse 150 Li a day. The slow horse goes 12 days first. How many days can the fast horse catch up with the slow horse?

150 × 12 ^ (240-150) = 1800 ^ 90, = 20 (days). A: fast horse can catch up with slow horse in 20 days