SOLUTION: A motor cycle covers 40 km with a speed of 20km /h find the speed of the motor -cycle for the next 40 km journey so that the average speed of the whole journey will be 30 km /h

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Question 1068642: A motor cycle covers 40 km with a speed of 20km /h find the speed of the motor -cycle for the next 40 km journey so that the average speed of the whole journey will be 30 km /h
Answer by josgarithmetic(39630) About Me  (Show Source):
You can put this solution on YOUR website!
                  SPEED        TIME               DISTANCE

First part          20        40%2F20                 40

Next part           r         40%2Fr                 40

Total                         40%2F20%2B40%2Fr            80


Average speed wanted 30 kilometer per hour.

80%2F%2840%2F20%2B40%2Fr%29=30
Simplify and solve this for r.

8%2F%282%2B40%2Fr%29=3
8=3%282%2B40%2Fr%29
4=3%281%2B20%2Fr%29
4=3%2B60%2Fr
4r=3r%2B60
highlight%28r=60%29