Multiple choice

A boat goes 24 km upstream and 28 km downstream in 6 hours. It goes 30 km upstream and 21 km downstream in 6.5 hours. Find the speed of the boat in still water and the speed of the stream (both in kmph).

  1. 9, 5

  2. 10, 4

  3. 12, 6

  4. None of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let u be upstream speed and d be downstream speed. 24/u + 28/d = 6 and 30/u + 21/d = 6.5. Solving this system, we find u = 6 and d = 14. Speed of boat = (d+u)/2 = 10, speed of stream = (d-u)/2 = 4.

AI explanation

Let the upstream speed be u and the downstream speed be d. We get the equations 24/u + 28/d = 6 and 30/u + 21/d = 6.5. Solving these equations gives u = 6 and d = 14. The speed of the boat in still water is (14 + 6) / 2, which is 10 kmph, and the speed of the stream is (14 - 6) / 2, which is 4 kmph.

Keep practicing — related questions