Question 470916
Distance (d) equals rate (r) times time (t) or d=rt; r=d/t and t=d/r

Time it takes to travel 10 kilometers at 30 kilometers per hour:
t=d/r=10/30=1/3 hour=20 min
Time it takes to travel 30 kilometers at 15 kilometers per hour:
t=d/r=30/15=2 hours
Total time for the trip=20 min + 2 hr=2 hr 20 min

Time it takes to travel 40 kilometers at 20 kilometers per hour:
t=d/r=40/20=2 hours
Total time for the trip =2 hr
Ans: 2 hr 20 min minus 2 hr=20 min
It takes him 20 min longer

Hope this helps--ptaylor