SOLUTION: 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 r

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Question 438062: 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?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
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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%2Fs + 80%2F%282s%29 = 3
multiply by 2s
2s*20%2Fs + 2s*80%2F%282s%29 = 2s(3)
Cancel the denominators, results
2(20) + 80 = 6s
40 + 80 = 6s
120 = 6s
s = 120%2F6
s = 20 mph, an incredible speed for a rowboat
:
:
Check solution using the time equation
20%2F20 + 80%2F40 =
1 + 2 = 3 hrs