Multiple choice

Find the time taken by the boat to cover 81.6 Km downstream and 70 Km upstream. I. Speed of the boat in still water is 250% more than the speed of the stream. II. Sum of the twice the speed of the boat in still water and thrice the speed of the stream is 40 Km/h III. Upstream speed of the boat is 10 Km/h.

  1. All I, II and III

  2. Any two of the three

  3. Only I and III

  4. Any one of the three

  5. Even I, II and III together are not sufficient
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let boat speed = b, stream speed = s. We need downstream and upstream times. From I: b = s + 2.5s = 3.5s. From II: 2b + 3s = 40. From III: b - s = 10. Any pair works: I+III: b = 3.5s and b - s = 10 gives 2.5s = 10, s = 4, b = 14. II+III: 2b + 3s = 40 and b = s + 10 gives 2(s+10) + 3s = 40, 5s = 20, s = 4, b = 14. I+II: b = 3.5s and 2b + 3s = 40 gives 7s + 3s = 40, s = 4, b = 14. All pairs yield same result.

Keep practicing — related questions