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 10 min. If the current in that part of

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Question 1092089: 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 10 min. If the current in that part of the river is 4 km per hr, what was her boat speed in still water?
Found 3 solutions by jorel1380, josmiceli, MathTherapy:
Answer by jorel1380(3719) About Me  (Show Source):
You can put this solution on YOUR website!
Let s be the speed of Jane's boat in still water. Then:
.25(s-4)=.2(s+4) (.25=1/4 hour=15 min; .2=1/5 hr=10 min)
.25s-1=.2s+.8
.05s=1.8
s=36
Jane's boat goes 36 kmh in still water
☺☺☺☺

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Convert minutes to hrs
+15%2F60+=+1%2F4+ hrs
+10%2F60+=+1%2F6+ hrs
Let +s+ = her speed in still water
-----------------------------------
Going upsteam:
(1) +d+=+%28+s+-+4+%29%2A%281%2F4%29+ km
Going downstream:
(2) +d+=+%28+s+%2B+4+%29%2A%281%2F6%29+ km
-------------------------------
+%28+s+-+4+%29%2A%281%2F4%29+=+%28+s+%2B+4+%29%2A%281%2F6%29+
Multiply both sides by +12+
+3%2A%28+s+-+4+%29+=+2%2A%28+s+%2B+4+%29+
+3s+-+12+=+2s+%2B+8+
+s+=+20+
The speed in still water is 20 km/hr
---------------------------------
check:
(1) +d+=+%28+20+-+4+%29%2A%281%2F4%29+
(1) +d+=+16%2F4+
(1) +d+=+4+ km
and
(2) +d+=+%28+20+%2B+4+%29%2A%281%2F6%29+
(2) +d+=+24%2F6+
(2) +d+=+4+ km
OK

Answer by MathTherapy(10555) 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 10 min. If the current in that part of the river is 4 km per hr, what was her boat speed in still water?
Let sped in still water be S

Then we get the following DISTANCE equation: %2815%2F60%29%28S+-+4%29+=+%2810%2F60%29%28S+%2B+4%29

%281%2F4%29%28S+-+4%29+=+%281%2F6%29%28S+%2B+4%29

%28S+-+4%29%2F4+=+%28S+%2B+4%29%2F6

6(S - 4) = 4(S + 4) ------- Cross-multiplying 

6S - 24 = 4S + 16

6S - 4S = 16 + 24

2S = 40

S, or speed in still water = highlight_green%28matrix%281%2C4%2C+40%2F2%2C+%22=%22%2C+20%2C+%22km%2Fh%22%29%29

IGNORE anyone who says otherwise!