You can put this solution on YOUR website!
Debbie traveled by boat 5 miles upstream to fish in her favorite spot.
Because of the 4 mph current, it took her 20 minutes longer to get there
than to return.
How fast will her boat go in still water?
Let s = boat speed in still water
(s-4) = speed upstream
(s+4) = speed down stream
Convert 20 min to hrs: 20/60 =
Write a time equation: time =
Upstream time = downstream time + 20 minutes (1/3 hr)
To clear out these denominators, multiply equation by 3(s+4)(s-4)
15(s+4) = 15(s-4) + (s+4)(s-4)
15s + 60 = 15s - 60 + s^2 - 16
0 = 15s - 15s - 60 - 60 + s^2 - 16
0 = s^2 - 136
s^2 = 136
s = 11.66 mph speed in still water
Check solution on calc: (speed up = 7.66 and speed down = 15.66)
5/7.66 - 5/15.66 = .3333 which is 1/3 of an hr