Multiple choice

Find the speed of the stream. (I) A boat can cover the distance in 5 hr. upstream. (II) It can cover the distance in 3 hr. downstream. (III) It covers the distance of 10 km.

  1. Only II

  2. Only III

  3. I & either II or III

  4. All the three are necessary

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Let boat speed = b, stream speed = s. Upstream: (b-s) × 5 = distance. Downstream: (b+s) × 3 = distance. Statement III gives distance = 10 km. Setting up: 5(b-s) = 10 and 3(b+s) = 10. This gives b-s = 2 and b+s = 10/3. Solving: 2b = 2 + 10/3 = 16/3, so b = 8/3. Then s = 10/3 - 8/3 = 2/3 km/hr. All three statements are necessary.

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