**Problem 4**

D and M were
one mile apart when they began walking toward each other. D walks at a constant
rate of 3mph, and M walks at a constant rate of 4 mph. When they started, D’s
dog, who ran at a constant rate of 7 mph, ran to M:
then turned back and ran to D. If the dog continued to run back and forth until
D and M met and lost no time turning around, how far did it run?

[Problem submitted by Iris
Magee, LACC Associate Professor of Mathematics.]

**Solution for Problem 4:**

1 mile. The distance between D and M is decreasing at
a rate of 7 mph, therefore it takes_{}of an hour for the distance to decrease from 1 mile to 0. In
this time the dog ran _{} mile.