You allow yourself 34 min to drive 26 mi to the airport, but you're caught in heavy traffic and average only 15 mi/h for the first 13 min . What must your average speed be on the rest of the trip if you're to make your flight?

Answer 1

you went 15/60 * 13 = 3.25 miles in first 13 min
so
26 - 3.25 = 22.75 miles left
and
34 - 13 = 21 minutes left which is 21/60 = .35 hours
so
22.75 miles/.35 hours = 65 mph