One boat travelling 15 mph goes 47 miles downstream in the same amount of time that another boat going 20 mph goes 40 miles upst
ream. How fast is the current in mph? (Round your answer to the nearest tenth of miles per hour and enter only the numerical part
1 answer:
Answer:
3.9 mi/h
Step-by-step explanation:
We assume that the given speeds are the speeds of the boats relative to the water. If c is the speed of the current, we have ...
time = distance/speed
47/(15 +c) = 40/(20 -c)
47(20 -c) = 40(15 +c) . . . . . . multiply by (20-c)(15+c)
940 -600 = 40c +47c . . . . . add 47c-600
340 = 87c . . . . . . . . . . . . . . . simplify; next divide by 87
c = 340/87 ≈ 3.9080 . . . . mi/h
The speed of the current is about 3.9 mi/h.
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