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    Hi,

    Two boys starting from the same place walk at a rate of 5kmph and 5.5kmph respectively. What time will they take to be 8.5km apart, if they walk in the same direction?

    Select an answer:
    A. 17 hrs
    B. 25 hrs
    C. 31 hrs
    D. 45 hrs

    Answer:
    Option
    A
    Explanation:
    The relative speed of
    the boys = 5.5kmph – 5kmph
    = 0.5 kmph
    Distance between them is 8.5 km
    Time= 8.5km / 0.5 kmph =
    17 hrs

    I understand the internet's solution but wonder why mine would not work:

    Boy 1: Rate 5 kmph x t = 5t (distance)

    Boy 2; Rate 5.5 kmph x t = 5.5t (distance):confused:

    Distance of Boy 1 + Distance of Boy 2 = 8.5 (apart)

    5t + 5.5t = 8.5
    10.5t = 8.5
    t = 0.809 hr.

    Obviously my solution is wrong but why? Is there a similar but correct that I could have used to mine?
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    It's not 5t + 5.5t = 8.5, it should be 5.5t - 5t = 8.5 since you're trying to find the difference, then you'd have the right answer.
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    (Original post by 0x2a)
    It's not 5t + 5.5t = 8.5, it should be 5.5t - 5t = 8.5 since you're trying to find the difference, then you'd have the right answer.
    Thanks, I guess it was obvious.
 
 
 
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