Question

On Jiamin's trip to Wisconsin, her average rate of speed for the whole 5-hour trip was 62 miles per hour. For the first two hours of her trip, she kept her average speed at 50 miles per hour Then she realized she was going to be late, so she started driving faster. What was her average speed for the last three hours of her trip?

Answer 1

After 2 hours, she was (62 mph -50 mph)*2h = 24 miles behind her trip average, so she had to make that distance up in the last 3 hours. That is, her average for the last 3 hours was (24 mi)/(3h) = 8 mph more than her trip average.

Jiamin averaged 62+8 = 70 mph for the last 3 hours of her trip.