A1. fast way: Let imagine that the speed of the river is very close to the speed of the swimmer. So, when the swimmer is swiming up it can take a very long time and it is obvious that x>>y. So, A

2. usual way:

let V - the speed of the swimmer

U - the speed of the river

L - length of the round trip

\(y=\frac{L}{V}\)

\(x=\frac{\frac12*L}{V-U}+\frac{\frac12*L}{V+U}=L*\frac{V}{V^2-U^2}>L*\frac{V}{V^2-0^2}=L*\frac{1}{V}=y\)

So, x>y

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