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    Question

    A takes 8 hours more than the time taken by B to cover a

    distance of 160 km. If A doubles his speed. he takes 3 hours more than B to cover the same distance. The speed (in km/h) of B is:
    A 72 Correct Answer Incorrect Answer
    B 80 Correct Answer Incorrect Answer
    C 70 Correct Answer Incorrect Answer
    D 75 Correct Answer Incorrect Answer

    Solution

    Time taken by A = 8 hours more than B Distance = 160 km A doubles the speed, he takes 3 hours more than B. Let the speed be SA and SB According to the question, ⇒ 160/SA – 160/SB = 8......(1) ⇒ 160/2SA – 160/SB = 3 ⇒ 80/SA – 160/SB = 3 ....(2) Multiplying equation (1) by 1/2 we get, ⇒ 80/SA – 80/SB = 4 .....(3) Now, Substituting equation (2) and (3) we get, ⇒ 80/SA – 160/SB = 3 and 80/SA – 80/SB = 4 ⇒ 160/SB – 80/SB = 4 – 3 ⇒ 80/SB = 1 ⇒ SB = 80 km/h ∴ The speed of B is 80 km/h.

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