<PRE><B>Question 438062</B>
Pete is planning to take a motorboat ride for 80 miles and then take a rowboat for another 20 miles.
 He figures his motorboat can travel at a rate that is twice as fast as he can row the rowboat.
 If he wants to take 3 hours for the trip, how fast will he row the rowboat?
:
Let r = speed of the rowboat
then
2r = speed of the motorboat
:
Write a time equation: time = dist/speed
:
Rowboat time + motor time = 3 hrs
{{{20/s}}} + {{{80/(2s)}}} = 3
multiply by 2s
2s*{{{20/s}}} + 2s*{{{80/(2s)}}} = 2s(3)
Cancel the denominators, results
2(20) + 80 = 6s
40 + 80 = 6s
120 = 6s
s = {{{120/6}}}
s = 20 mph, an incredible speed for a rowboat
:
:
Check solution using the time equation
{{{20/20}}} + {{{80/40}}} = 
1 + 2 = 3 hrs
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