SOLUTION: A boy started on a trip across a lake by a motorboat. After he had traveled 15 km, the motor failed and he had to use a banca for the remaining 6 km to his destination. His average

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Question 709372: A boy started on a trip across a lake by a motorboat. After he had traveled 15 km, the motor failed and he had to use a banca for the remaining 6 km to his destination. His average speed by motorboat was 4 km per hour faster than his average speed while rowing a banca. If the entire trip took 5 1/2 hours, what was his average speed while rowing?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
r, speed of the banca while rowing.
Units are kilometers per hour, and kilometers.
Vehicle____________rate___________time_______________distance
Motorboat__________r+4____________15%2F%28r%2B4%29___________15
Banca_______________r_____________6%2Fr________________6
TOTAL_____________________________5%261%2F2____________21

The sum of the times during use of each vehicle is the total traveling time of 5%261%2F2 hours. The only variable in that equation is r, the speed of the banca. (Rowing done in the banca). Motorboat speed would be r+4.

15%2F%28r%2B4%29%2B6%2Fr=5%261%2F2, find r.