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SSC Selection Post 2019 PYQ — Question 51

SSC Selection Post - Higher Secondary Level 2019 - 15 Oct 2019 • Quantitative Aptitude • Q51

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A man travels a distance of 4 km every day. One day he increases his speed by 0.8 km/h than usual speed and reaches his destination 15 minutes earlier. What is the normal speed of the man?

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Correct answer: C

Explanation

The correct answer is option 3 i.e. 3.2 km/h.

Let the usual speed be x km/h.

Normal time = 4x \frac{4}{x} hours

Time after change in speed = 4x+0.8\frac{4}{x + 0.8} hours

4x−4x+0.8=0.25\frac{4}{x} - \frac{4}{x + 0.8} = 0.25

⇒ 4(x + 0.8) - 4x = 0.25x(x + 0.8)

⇒ 4x + 3.2 - 4x = 0.25x(x + 0.8)

⇒  3.2 = 0.25x(x + 0.8)

⇒ 12.8 = x(x + 0.8)

⇒ x2 + 0.8x - 12.8 = 0

⇒ (x - 3.2)(x + 4) = 0

⇒ x = 3.2