Expert: Scott A Wilson - 11/4/2009

Question
Need help with how to set up following equation.
Fred begins walking towards John's house at 3miles/hr.  John leaves his house at the same time and walks towards Fred's house at 2miles/hr.  How long will it be before they meet, if the distance between the houses is 4 miles?

Answer
It would be the same as if we asked how long it would take on to get across if they walked at (3+2) mph, which is 5 mph.  For someone going 5 mph to go 4 miles, it takes 48 minutes (that's 4/5 of an hour).

To check this out, after 48 minutes, Fred would have gone 12/5 of a mile.
After 48 minutes, John would have gone 8/5 of a mile.

When the distances are added together, that gives (12+8)/5 = 20/5 = 4 miles.