9514 1404 393
Answer:
4 mph
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.