SarkariPYQ

SSC CPO 2019 PYQ — Question 103

SSC CPO Tier I - 13th December 2019 - Shift 1 • Quantitative Aptitude • Q103

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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 km/hr, then the speed of the boat in still water, in km/hr, is:

Show answer & explanation

Correct answer: D

Explanation

The correct answer is Option 4 i.e. 12

Concept Application

If the speed of a boat in still water is u km/hr
and the speed of the current is v km/hr, then

Speed downstream

= (u + v) km/hr

Speed upstream

= (u - v) km/hr

Given u = 9 km/hr

Therefore,

{10.5/(u + 9)} + {10.5/(u - 9)} = 4

⇒ 4u2 - 21u - 324 = 0

After solving the quadratic equation,

u = 12 or 27/4

As options given,

u = 12 km/hr