The paddling rate of Alvin is 9km/hr
Given time against the  river current is 10 hours , speed is 3km/hr
and time with the river current given is 5 hours and the speed is 3km/hr
We need to calculate the paddling rate of Alvin
Let us assume that
r =Alvin's average paddling rate in km/hour
y = speed of the current in km/hour
we know that
speed= distance/time
∴ distance=speed*time
Now,
To Campsite against the current
Speed=(r-y)
∴ Speed=(r-3) ---- (1)
Time=8 hours
Distance=(r-3)*10------ (2)
10r - 30
From Campsite with the current
Speed=(r+y)
∴Speed=(r+3)*5
Time=3 hours
Distance=(r+3)*5----(1)
Equate equation 1 and equation 2
5r +15
because is the same distance
5r + 15 = 10r - 30
5r = 45
r = 9
Hence ,The rate of the paddling rate is 9km/hr
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