Suzanne is exercising on a treadmill. She first runs at a speed of 6 miles per hour for 10 minutes and then she jogs at a speed of 3 miles per hour for 5 minutes. What is her average speed while exercising on the treadmill?
[6 m/hr x 1/6 hr + 3 m/hr X 1/12 hr] / (1/6 + 1/12 hr) = ....... m/hr average