SOLUTION: a motorboat took 2 hours to make a downstream trip witha 5 mph current. the return trip against the same current too 4 hours. find the speed of the boat in still water.

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: a motorboat took 2 hours to make a downstream trip witha 5 mph current. the return trip against the same current too 4 hours. find the speed of the boat in still water.      Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


    

Question 414524: a motorboat took 2 hours to make a downstream trip witha 5 mph current. the return trip against the same current too 4 hours. find the speed of the boat in still water.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let s = the speed of the boat in still water in mi/hr
Let d = the one-way trip in miles
Going downstream, speed = s+%2B+5 mi/hr
Going upstream, speed = s+-+5 mi/hr
given:
downstream:
d+=+%28s+%2B+5%29%2A2
upstream:
d+=+%28s+-+5%29%2A4
--------------
d is the same in both equations
%28s+%2B+5%29%2A2+=+%28s+-5%29%2A4
2s+%2B+10+=+4s+-+20
2s+=+30
s+=+15
The speed of the boat in still water is 15 mi/hr
check:
d+=+%2815+%2B+5%29%2A2
d+=+40
upstream:
d+=+%2815+-+5%29%2A4
d+=+40
OK