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# The distance between two points is 36 km. A boat rows in still water at 6 kmph. It takes 8 hours less to cover this distance in downstream in comparison to that in upstream. The rate of stream is

 A) 3 kmph B) 2 kmph C) 2.5 kmph D) 4 kmph

 A) 3 kmph

Description for Correct answer:
Speed of current = x kmph

$$\Large \therefore$$ Rate downstream

= (6 + x) kmph

Rate upstream = (6 - x) kmph

$$\Large \therefore \frac{36}{6 - x} - \frac{36}{6 + x} = 8$$

=> $$\Large 36(\frac{6 + x - 6 + x}{(6 - x)(6 + x)}) = 8$$

=> $$\Large \frac{36 \times 2x}{(6 - x)(6 + x)} = 8$$

=> $$\Large 9x = 36 - x^{2}$$

=> $$\Large x^{2} + 9x - 36 = 0$$

=> $$\Large x^{2} + 12x - 3x - 36 = 0$$

=> $$\Large x(x + 12) - 3(x + 12) = 0$$

=> $$\Large (x - 3) (x + 12) = 0$$

=> x = 3 kmph

Part of solved Aptitude questions and answers : >> Aptitude

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