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A paddling canoeist took 2 h to travel 12 km down a river, with the current. It took 4 h to do the return trip up the river, against the current. What was the speed of the current

 Feb 4, 2020
 #1
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12 / 2 = 6 km/h - his speed with the current
12 / 4 = 3 km/h - his speed against the current.
[6 - 3 ] / 2 =1.5 km/h - the speed of the current. 

 Feb 4, 2020
 #2
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Call the current spped, C

Call the speed of the  boat in still water, R

 

Effective rate with current  =  R + C

Effective rate against the current  = [ R - C ]

 

So  we have that  distamce / rate   = time...so...

 

12/ [ R + C]   = 2             12  /[ R - C]  =  4

12 = 2 [ R + C]                12  = 4 [ R - C]

6  = R + C                        3 = R - C

 

Add the last two  equations

 

9 = 2R

4.5 = R

 

And 

 

6 = R + C

6 = 4.5 + C

1.5   = C

 

cool cool cool

 Feb 4, 2020

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