SOLUTION: Jane took 15 min to drive her boat upstream to​ water-ski at her favorite spot. Coming back later in the​ day, at the same boat​ speed, took her 5 min. If

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Question 1093796: Jane took
15 min to drive her boat upstream to​ water-ski at her favorite spot. Coming back later in the​ day, at the same boat​ speed, took her
5 min. If the current in that part of the river is
2 km per​ hr, what was her boat speed in still​ water?
Found 4 solutions by josgarithmetic, josmiceli, MathTherapy, greenestamps:
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
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Jane took
15 min to drive her boat upstream to​ water-ski at her favorite spot. Coming back later in the​ day, at the same boat​ speed, took her
5 min. If the current in that part of the river is
2 km per​ hr, what was her boat speed in still​ water?
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15 minutes is 1%2F4hour.
5 minutes is 1%2F12hour.
r, boat speed in still water.
Distance each way is the same , both directions.

highlight_green%28%28r-2%29%2A%281%2F4%29=%28r%2B2%29%2A%281%2F12%29%29

4kilometers%2Fhour

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
+c+=+2+ = the speed of the current in km/hr
Let +s+ = the speed of the boat in still water
+s+%2B+2+ = the speed of the boat going downstream
+s+-+2+ = the speed of the boat going upstream
Let +d+ = one-way distance she travels
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Convert minutes to hrs
going upstream:
(1) +d+=+%28+s+-+2+%29%2A%281%2F4%29+
going downstream:
(2) +d+=+%28+s+%2B+2+%29%2A%281%2F12%29+
------------------------------
Set (1) = (2)
+%28+s-2+%29%2A%281%2F4%29+=+%28+s%2B2+%29%2A%281%2F12%29+
Multiply both sides by +12+
+3%2A%28+s-2+%29+=+s+%2B+2+
+3s+-+6+=+s+%2B+2+
+2s+=+8+
+s+=+4+
The speed of the boat in still water is 4 km/hr
--------------------------
check answer:
(1) +d+=+%28+4+-+2+%29%2A%281%2F4%29+
(1) +d+=+1%2F2+ km
and
(2) +d+=+%28+4+%2B+2+%29%2A%281%2F12%29+
(2) +d+=+6%2F12+
(2) +d+=+1%2F2+ km
OK

Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!
Jane took
15 min to drive her boat upstream to​ water-ski at her favorite spot. Coming back later in the​ day, at the same boat​ speed, took her
5 min. If the current in that part of the river is
2 km per​ hr, what was her boat speed in still​ water?
FYI: Speed in still water IS NOT matrix%281%2C2%2C+2%262%2F3%2C+%22km%2Fh%22%29, as one person claims. 

The correct speed is: highlight_green%28matrix%281%2C2%2C+4%2C+%22km%2Fh%22%29%29

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!

So many different ways to solve the same problem....!

Here is what I would do.

The trip took 3 times as long going upstream as downstream. That means her downstream speed must be 3 times her upstream speed.

If b is the speed of her boat in still water, then her upstream speed is b-2 and her downstream speed is b+2. So

b%2B2+=+3%28b-2%29
b%2B2+=+3b-6
8+=+2b
b+=+4