Bob was driving home at an average speed of 40mph for 2 hours. How fast should he drive for the next 1 hour to have an average speed of 50mph?
Distance / Time = Rate
Let R be the rate we are looking for ...so.....
[ 40(2) + R(1) ]
_______________ = 50 simplify
3
80 + R = 50 * 3
80 + R = 150 subtract 80 from both sides
R = 70 (mph)
