Multiple choice

A boat takes 20 hours to cover a certain distance upstream and come back to the starting point downstream. If the speed of the boat in still water is 8 km/hr what is the distance it covers upstream?

  1. 84 km

  2. 78 km

  3. 66 km

  4. 52 km

  5. Data inadequate
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Let the distance be D km and stream speed be S km/hr. Upstream speed = 8-S, downstream speed = 8+S. Time = D/(8-S) + D/(8+S) = 20. This gives D(16)/(64-S²) = 20. Without knowing S, we cannot determine D uniquely. Different values of S give different D (e.g., S=1 gives D≈79, S=2 gives D≈60). The data is inadequate.

Keep practicing — related questions