The cow, the horse, and the sheep (John after Dudeney and Loyd)
Here is a twist to an old problem which, to my surprise, seems not to have appeared before.
A farmer has a field, a cow, a horse, and a sheep. The cow and the horse together can graze the field bare in three days, the cow and the sheep in four days, the horse and the sheep in six days, and all three in just two days. How many days would it take each animal to graze the field bare on its own?
For the solution, and some notes on the history of the problem, click here.