Systems’ Application problem

Question

a race car driver averaged 150 miles per hour over the first part of the race, but engine trouble dropped her average speed to 100 miles per hour for the rest of the race. if the 500- mile race took the driver 4 hours to complete, after what period did her engine trouble start?

Answer 1

distance = rate x time, so

$500=150t+100(4-t)$

Solve for t.