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

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) (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
Banca_______________r_____________________________6
TOTAL_________________________________________21

The sum of the times during use of each vehicle is the total traveling time of 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.

, find r.
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