Rob left Mark's house and drove toward the dump at an average speed of 45 km/h James left later driving in the same direction at an average speed of 75 km/h. After driving for 3 hours James caught up. How long did Rob drive before James caught up?

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Answer 1 · 2016-03-20T13:44:24

The distance they traveled was the same. The only reason Rob traveled so far was he had a head start, but since he was slower, it took him longer.

Answer is 5 hours.

Total distance based on James' speed:

#s=75*3# #(km)/cancel(h)*cancel(h)#

#s=225km#

This is the same distance Rob traveled, but at a different time, since he was slower. The time it took him was:

#t=225/45# #cancel(km)/(cancel(km)/h)#

#t=5h#