Question 283714
THE CURRENT IN A RIVER IS 4MPH. A BOAT MOTORS 6 MILES UPSTREAM IN THE SAME TIME IT TAKES TO GO 12 MILES DOWNSTREAM. SPEED OF BOAT IN STILL WATER?
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Upstream DATA:
distance = 6 miles ; rate = b-4 mph ; time = 6/(b-4) hrs
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Downstream DATA:
distance = 12 miles ; rate = b+4 mph ; time = 12(b+4) hrs
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Equation:
time up = time down
6/(b-4) = 12/(b+4)
1/(b-4) = 2/(b+4)
b+4 = 2(b-4)
b+4 = 2b-8
b = 12 mph (boat speed in still water)
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Cheers,
Stan H.