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A motorboat can maintain a constant speed of 47 mph relative to the water. The boat makes a trip upstream to a certain point in 51 minutes; the return trip takes 43 minutes. What is the speed of the current?

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sqdancefan

9514 1404 393

Answer:

  4 mph

Step-by-step explanation:

The ratio of speeds upstream and down is inversely proportional to the ratio of times upstream and down. If we let c represent the speed of the current, the relation can be written ...

  (47 +c)/(47 -c) = 51/43

  43(47 +c) = 51(47 -c)

  94c = 8(47) . . . . . . . . . . . add 51c -43(47)

  c = 4 . . . . . divide by 94

The speed of the current is 4 miles per hour.