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2018 · Q46

A man can row at a speed of x km/hr in still water. If in a stream which is flowing at a speed of y km/hr it takes him z hours to row to a place and back, then what is the distance between the two places?

Elementary MathematicsTime, Speed and Distance
  1. Az(x² - y²)/2y
  2. Bz(x² - y²)/2x
  3. C(x² - y²)/2zx
  4. Dz(x² - y²)/x

Explanation

If d is the one-way distance: d/(x + y) + d/(x − y) = z. Combining gives 2xd/(x² − y²) = z, so d = z(x² − y²)/(2x), option (B).