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 = 13−x13+x = 49
By solving, x=5
Upstream speed = 8 mph & downstream speed = 18 mph
Time for 60 miles upstream = 608 = 7 Hours 30 mins
Time for 60 miles downstream = 6018 = 3 Hours 20 mins
Diff = 4 Hours 10 minutes
Answer E
So here the upstream speed acts as resistance?