SOLUTION: it takes a boat 2 hours to travel 24 miles downstream and 3 hours to travel 18 miles upstreat. what is the speed of the boat in still water and of the current river?

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Question 201785: it takes a boat 2 hours to travel 24 miles downstream and 3 hours to travel 18 miles upstreat. what is the speed of the boat in still water and of the current river?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let b = speed of boat in still water
Let c = speed of current
Upstream:
Speed is b+-+c
d%5Bu%5D+=+%28b+-+c%29%2At%5Bu%5D
Downstream:
speed is b+%2B+c
d%5Bd%5D+=+%28b+%2B+c%29%2At%5Bd%5D
given:
d%5Bu%5D+=+18
t%5Bu%5D+=+3
d%5Bd%5D+=+24
t%5Bd%5D+=+2
------------------
(1) 18+=+%28b+-+c%29%2A3
(2) 24+=+%28b+%2B+c%29%2A2
and
(1) 18+=+3b+-+3c
(2) 24+=+2b+%2B+2c
Multiply both sides of (1) by 2
Multiply both sides of (2) by 3
(1) 36+=+6b+-+6c
(2) 72+=+6b+%2B+6c
Add (1) and (2)
108+=+12b
b+=+9
And, from (1),
18+=+3%2A9+-+3c
3c+=+27+-+18
3c+=+9
c+=+3
The speed of the boat in still water is 9 mi/hr
The speed of the current is 3 mi/hr
check:
(1) 18+=+%289+-+3%29%2A3
(2) 24+=+%289+%2B+3%29%2A2
and
(1) 18+=+6%2A3
18+=+18
(2) 24+=+12%2A2
24+=+24
OK