Question

A swimmer is swimming across a river that is exactly one mile wide, and the river current is 1.5 mph directly south. If the swimmer can swim through still water at 2.5 mph, and he swims east, perpendicular to the north-south bank, how far downstream will he be carried by the current as he swims across?

Answer 1

he will take 1/2.5 = 0.4 hours to cross the river.
In that time, he will be carried 0.4 * 1.5 = 0.6 miles downstream.