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]