A takes 30 minutes more than B to cover a distance of 15 km at a certain speed. But if A doubles his speed, he takes one hour less than B to cover the same distance. What is the speed (in km/h) of B?
Show answer & explanation
Correct answer: C
Explanation
Correct Answer is option 3 i.e. 6
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Understanding |
Application |
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Let A’s speed = a km/h, B’s speed = b km/h |
According to question: 15(1/a – 1/b) = 30/60 ⇒ 1/a – 1/b = 1/30 ……………..(1) And 15(1/b – 1/2a) = 1 ⇒ 1/b – 1/2a = 1/15……………...(2) Adding both equations: ⇒ 1/2a = 3/30 = 1/10 ⇒ a = 5 Then, b = 6 Hence, speed of B = 6 km/hr |