a boat can travel 5 miles downstream in the same length of t

a boat can travel 5 miles downstream in the same length of time it travels 3 miles upstream. if the rate of the current is 3mph, find the speed of the boat in still water.
d=5 ?
r=3mh ?
t=?

Solution

Downstream DATA:
distance = 5 miles ; rate = b+3 mph ; time = d/r = 5/(b+3) hrs
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Upstream DATA:
distance = 3 miles ; rate = b-3 mph ; time = d/r = 3/(b-3)
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Equations:
time up = time down
3/(b-3) = 5/(b+3)
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3(b+3) = 5(b-3)
3b+9 = 5b-15
2b = 24
b = 12 mph (speed of the boat in still water)