SOLUTION: The current in the river flowed at 3 miles per hour. The boat could travel 24 miles downstream in one-half the time it took to travel 12 miles upstream. What was the speed of the b

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Question 67295This question is from textbook An Incremental Development
: The current in the river flowed at 3 miles per hour. The boat could travel 24 miles downstream in one-half the time it took to travel 12 miles upstream. What was the speed of the boat in still water?This question is from textbook An Incremental Development

Answer by ankor@dixie-net.com(12700) About Me  (Show Source):
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The current in the river flowed at 3 miles per hour. The boat could travel 24 miles downstream in one-half the time it took to travel 12 miles upstream. What was the speed of the boat in still water?
:
Let s = speed in still water
:
Speed upstream: (s-3)
Speed downstream: (2+3)
:
Write a time equation: time = dist/speed
:
Time 24 mi downstream = half the time 12 mi upstream
24%2F%28%28s%2B3%29%29 = .5%2812%2F%28%28s-3%29%29%29
:
24%2F%28%28s%2B3%29%29 = 6%2F%28%28s-3%29%29
:
Cross multiply:
24(s-3) = 6(s+3)
24s - 72 = 6s + 18
24s - 6s = 18 + 72
18s = 90
s = 90/18
s = 5 mph in still water
:
:
Check:
24/8 = 3hr for 24 mi downstream
12/2 = 6hr for 12 mi upstream