Only one blacksmith at a time can work on a given horse, so to maximize efficiency they must split up. This means that in any given five-minute interval eight horses are being shod and two are standing idle. If it takes 20 minutes to shoe each horse, and the whole job must be completed in 25 minutes, then no horse can stand idle for more than one five-minute interval. Can this be arranged?
Yes. If there are five time intervals, and two horses are idle in each interval, then each of the 10 horses can be assigned a single idle interval:
From The Inquisitive Problem Solver, 2002.
