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slavikrds [6]
3 years ago
5

The speed of a river current is 7 mph. If a boat travels 20 miles downstream in the same time that it takes to travel 10 miles u

pstream find the speed of the boat in still water
Mathematics
1 answer:
dem82 [27]3 years ago
3 0

Answer:

  21 mph

Step-by-step explanation:

The relationship between time, speed, and distance is ...

  time = distance/speed

The speed downstream is b+7 if the boat's speed is b. The speed upstream is b-7, and the times in each direction are equal. This means ...

  20/(b+7) = 10/(b-7) . . . . . . time in each direction are the same

  20(b-7) = 10(b+7) . . . . . . . cross multiply

  (20-10)b = 7(10+20) . . . . . add 7(20)-10b

  b = 7(20 +10)/(20 -10) = 21 . . . . mph

The speed of the boat in still water is 21 mph.

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