Question

10) Spike drives for 50 miles at 60mph. He slows down and travels

another 50 miles at 40mph. For the final part of the 120 mile journey,
he speeds up to 80mph. How long does he take altogether? What is
his average speed (to the nearest mph)?
​

Answer 1

2 1/3 hours or 2 hours 20 minutes.

51.4 mph to 1 decimal place.

Explanation:

Time = distance speed

First 50 miles time taken = 50 / 60 = 5/6 hours

Second 50 miles - time = 50/40 = 5/4 hours.

Final 20 miles - time taken = 20 / 80 = 1/4 hours.

Total time taken = 5/6 + 5/4 + 1/4

= 5/6 + 6/4

= 10/12 + 18/12

= 28/12

= 7/3 or 2 1/3 hours or 2 hours 20 minutes.

Average speed = total distance / total time

= 120 / 7/3

= 120 * 3/7

= 51.4 mph to 1 decimal place.