Problema Solution
Kevin is looking into rowing. He can row his boat at a near by river. A trip down stream will take him 3 hours. The return trip, against the current, will take him 5 hours. If the total mileage for the round trip is 60 miles, how fast is the river current?
Answer provided by our tutors
Speed = distance\time
The current is x mph, he can paddle y mph.
Total distanced travelled was 60 miles, it was a trip to/from the same point, therefore each leg of the trip was 60/2=30 miles.
Downstream (current is helpful and positive), we have:
30 = (x + y) * 3
Upstream (current is fighting him and negative), we have:
30 = (x - y)*5
Setting these equations equal to each other:
(x+y)*3 = (x-y)*5
3x+3y = 5x-5y
8y=2x
x=4y
he is paddling four times faster than the current and we replace 'x' in the original equations with '4y':
30=(4y+y)*3 = 5y*3=15y
30=(4y-y)*5=3y*5=15y
30=15y, therefore y= 30/15 = 2
The current is 2mph