2. A competitive rowing team can travel 28 miles upriver in the same time it takes to travel 36 miles downriver. If the speed of the current is 4 mph, how fast can the team row in still water?

Question

1.      A competitive rowing team can travel 28 miles upriver in the same time it takes to travel 36 miles downriver. If the speed of the current is 4 mph, how fast can the team row in still water?

Answer 1

Let S be the speed of the team in still water, and t is the time they spend on both upriver row and downriver row, then

(S+4)t=36

(s-4)t=28

solve this equation group of two unknowns, we get S = 32.

Answer 2

Let's say I can row 3 mph in still water. Going downstream, I'm going to travel 3 + 4 = 7 mph. Going upstream, I'm actually going downstream, backward 1 mph.

d = rt, so t = d/r and the times are equal.

28/(r - 4) = 36/(r + 4)

28(r + 4) = 36(r - 4)

28r + 112 = 36r - 144

-8r = -256

r = 32 mph