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A boat takes 4 hours to travel from a place X to Y downstream and back from Y to X upstream. If the distance from X to Y is 10.5 km, and the speed of the current is 9 -

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Question

A boat takes 4 hours to travel from a place X to Y downstream and back from Y to X upstream. If the distance from X to Y is 10.5 km, and the speed of the current is 9 km/h, then the speed of the boat in still water, in km/h, is:

Options

  • `10 1/2`

  • 15

  • 12

  • `12 1/2`

MCQ

Solution

12

Explanation:

`10.5/(x + 9) + 10.5/(x - 9)` = 4

[Put your option to solve for 'x']

`10.5 [(x - 9 + x + 9)/(x^2 - 81)]` = 4

`21x = 4x^2 - 324`

`4x^2 - 21x - 324` = 0

`x = 12, (-27)/4`

This is not possible.

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Boats and Streams (Entrance Exam)
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