how much time did they spend walking

Question

Tyler and Pearl went on a 20 kilometer bike ride that lasted 3 hours. Because there were so many steep hills on the bike ride, they had to walk for most of the trip. Their walking speed was 4 kilometers per hour. Their riding speed was 12 kilometers per hour. How much time did they spend walking?

Answer 1

rate*time = distance.  If they spent t hours walking, they spent 3-t hours riding:

 

(4 kph)*(t hours) + (12 kph)*(3-t hours) = 20 km

 

4t + 36 - 12t = 20

 

Solve for t.