Bob is having a nice camping/fishing trip along a river. He leaves his campsite early in the morning, and gets on his boat, heading full throttle upstream.
After going for exactly one mile, his hat flips off of his head, and starts floating downstream. Bob doesn't realize that his hat has fallen off for five minutes, but then he notices that it's missing, and turns full throttle downstream.
He finally catches the hat at exactly the same spot as he camped that morning. The question is, how fast was the water traveling?
(Assume that he travels the same speed the entire time and that there is no turn around time.)
(In reply to
re: General Shortcut Formula by Vinodhan Selvarajalu)
While he is travellng upstream, remember he is travelling slower when compared to when he is travelling downstream. This can be mathematically wrtten as:
Relative speed of the boat when travelling u/s = (boat speed - river speed)
Relative speed of the boat when travelling d/s = (boat speed + river speed)
Hence he will cover more distance in 5 minutes travelling d/s compared to the same time travel along u/s. This accounts for the extra distance he covers.
re(2): General Shortcut Formula
