The ferry boat problem

The two ferry boats started from opposite sides of the river at the same instant. They ply the same route. One boat, however, was faster than the other, so they met at a point just 720 yards from the nearest shore. Each boat reached their destination and remained there for 10 minutes to change passengers and then started on its return trip. during their return trip they met at a point just 400 yards from the other shore. How wide is the river?

This is a puzzle by Samuel Loyd, an American puzzle author, and recreational mathematician popularly known as Sam Loyd. Loyd famously made the following comment about this puzzle in his book Cyclopedia of 5000 Puzzles, Tricks, and Conundrums - “Just to show how the average mortal follows the cut and dried rules for doing ordinary calculations and will be puzzled by simple problems which call for original lines of thought, attention is called to this practical example which requires only a slight knowledge of the most elementary arithmetic. By a kindergarten process it can be explained in a few minutes so that any child can do it, and yet I hazard the opinion that ninety-nine out of every one hundred of our shrewdest business men would fail to figure it out in a week. So much for learning mathematics by rule instead of common sense which teaches the reason why!” 

Solution