Audrey rode her bike to school at a rate of 12mi/hr. She rode back at a rate of 8mi/hr. How far is it to school if the round trip takes 1 hour?
Let us have d= the distance from home to school. Then the time at 12mi/hr is 5d because 12/60=1/5. Similarily 8/60=2/15 so it takes 15/2*d. Adding the times gives us 12.5d=60 so d=4.8mi. Thus it takes 4.8mi to school.
Let the distance = D
Average speed = Distance travelled / Time
Time = Distance / speed
D/12 + D/8 = 1 hour, solve for D
[2D + 3D] / 24 = 1 hour cross multiply
5D = 24 divide both sides by 5
D = 24/5
D = 4.8 miles - the distance from her home to shchool.