Multiple choice

Boat X covers a certain distance downstream in (b - 4) hours, and the same distance upstream in (b + 4) hours. The speed of the boat X in still water is 15 km/hr. The speed of boat Y in still water is equal to the speed of the stream, which is 6 km/hr. Find the distance (in km) covered by boat Y downstream in (b + 2) hours. Assume both boats are operating in the same stream conditions.

  1. 184

  2. 172

  3. 144

  4. 132

  5. 116
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let distance be D and stream speed be s=6. Boat X: (15+6)(b-4) = (15-6)(b+4). 21b - 84 = 9b + 36, so 12b = 120, b = 10. Distance D = 21 * (10-4) = 126 km. Boat Y speed in still water is 6 km/hr. Downstream speed of Y = 6+6 = 12 km/hr. Distance covered in (10+2) hours = 12 * 12 = 144 km.

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