A river is flowing downstream at a rate of 2 metres per second. Brendan, who has an average swimming speed of 3 metres per second, decides to go for a swim in the river. He dives into the river and swims downstream to a certain point, then swims back...?

Question

...upstream to the starting point. The total time taken is 4 minutes. How far did Brendan swim downstream?

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Answer 1 · 2017-09-28T10:41:24

Branden swimed #200 # metres downstream.

Brenden's swiming speed in downstream is #3+2=5# metres/sec

Brenden's swiming speed in upstream is #3-2=1#metre/sec

Let the distance from starting point to returning point is #x# metres

Total time taken to cover both upstream and downstream is

#4*60=240# seconds. (Given)

Time taken to cover downstream swiming is #x/5#seconds

Time taken to cover upstream swiming is #x/1 #seconds

Total time taken to cover both upstream and downstream is

# (x/5+x )#seconds , which is equal to 240 seconds.

#:.x/5+x =240 or (6x)/5 =240 or x=(5*240)/6=200 # metres

Branden swimed #200 # metres downstream. [Ans]