math
posted by Larry on .
Phil is making a 40kilometer canoe trip. If he travels at 30 kilometers per hour for the first 10 kilometers, and then at 15 kilometers per hour for the rest of the trip, how many minutes more will it take him then if he travels the entire trip at 20 kilometers per hour?

>he travels at 30 kilometers per hour for the first 10 kilometers
It takes 10/30 = 1/3 hour = 20 minutes
>at 15 kilometers per hour for the rest of the trip
The rest of the trip = 4010=30km,
which takes 30/15=2 hours
So, in total the first option takes 2 hours and 20 minutes or 2 1/3 hours.
The second option:
>he travels the entire trip at 20 kilometers per hour
40/20=2 hours
>how many minutes more will it take
2 1/3  2 =1/3 hour = 20 minutes
see you at ascii_org_ru 
time = distance/speed
10/30 + 30/15 = 2 1/3
40/20 = 2
so, it takes 1/3 hour (20 minutes) more.