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(22740) About Me  (Show Source):
You can put this solution on YOUR website!
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