rx10 wrote:
Speed of boat in still water = 13mph
Ratio of upstream & downstream = 4:9
Important :
Upstream speed = speed of boat - speed of stream
Downstream speed = speed of boat + speed of stream
Let's take speed of stream = \(x\)
Upstream speed = \(13 - x\)
Downstream speed = \(13 + x\)
Ratio = \(\frac{13-x}{13+x}\) = \(\frac{4}{9}\)
By solving, \(x = 5\)
Upstream speed = 8 mph & downstream speed = 18 mph
Time for 60 miles upstream = \(\frac{60}{8}\) = 7 Hours 30 mins
Time for 60 miles downstream = \(\frac{60}{18}\) = 3 Hours 20 mins
Diff = 4 Hours 10 minutes
Answer E
So here the upstream speed acts as resistance?