math

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if i drive home with a speed of 60km/h,I will arrive an hour ealier than expected.If i drive 40km/h then i will arrive an hour later than expected.At what speed should i travel in order to arrive BANG on time?

  • math -

    time to go home at 40 km/h --- d/40 hours
    time to go home at 60 km/h --- d/60 hours

    d/40 - d/60 = 2 (there is a 2 hr difference in the two times)
    time 120
    3d - 2d = 240
    d = 240

    so the two times are 240/40 and 240/60
    or 6 and 4 hours,
    so he wants to take 5 hours
    speed = 240/5 = 48 km/h

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