Question 1048257
d = r*t divide both sides by t
r = d/t
:
Downstream speed per hour: 34+r
Upstream speed per hour: 34-r
According to the formula:
80/34-r = 100/34+r  Cross multiply
80(34+r) = 100(34-r)
2720+80r = 3400-100r
80r+100r = 3400-2720
180r = 680
r = 3.78 This is the speed of the current.
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Check - In still water, their times would have been:
34+3.78 = 37.78; 100/37.78 = 2.65 
34-3.78 = 30.22; 80/30.22 = 2.65
Correct.
John