math

an express train makes a run of 240 km at a certain speed. another train whose speed is 12km/hr less takes an hour longer to cover the same distance. find the speed of the express train in km/hr.

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  1. speed of express ---- x km/h
    speed of slow train -- x - 12 km/h

    solve for x

    240/(x-12) - 240/x = 1

    (saying: the difference in their times = 1 hr
    and time = distance/rate )

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  2. v t = 240 so t = (240/v)

    (v-12) (t+1) = 240
    ====================

    v t - 12 t + v - 12 = 240
    or
    v + vt -12 t = 252
    substitute
    v +240 - 12(240/v) = 252

    v^2 - 12 v - 2880 = 0

    (v-60)(v+48) = 0
    v = -48 simply will not do
    so
    v = 48 km/hour

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  3. 60 km/hour

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  4. How can it be 48 ,it must be less than the other train

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  5. I donot understand

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  6. Even now i donot understand

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  7. Ya the answer is right u can check it

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  8. Ya that's right u all can check it

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