Speed Time & Distance math word problem.

Question

Bob started driving at 72 km/h for the first 4/9 of his trip. He later increased his speed by 3 km/h during the last 60 km of his trip. How many hours did his whole trip take?

Answer 1

We went 72 kph for 4/9 of the distance.  The rest of the trip will be a distance of (5/9)d

where d represents the total distance travelled.

 

(5/9)d = 60 km distance for 2nd part

 

Total distance = 60(9/5) = 108 km

 

(4/9)(108) = 48km for first part of the trip

 

So:  We went 72 kph for 48 km, then 75 kph for 60 km

 

d = rt

 

Part 1:

48 = 72t 

t = 48/72 = 2/3 hours = 40 minutes

 

Part 2:

60 = 75t

t = 60/75

t = 0.8 hours = (0.8 hours)(60 mins/hour) = 48 minutes

 

Total time:  40 minutes + 48 minutes = 88 minutes = 1 hour 28 minutes