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Math Help - Average speed question

  1. #1
    Senior Member Mukilab's Avatar
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    Average speed question

    A delivery lorry covers its outward journey at 50mph.
    It returns, over exactly the same distance at 33.3333mph.
    What is the lorry’s average speed over the entire journey?

    Not allowed to use a calculator. I would place the common denominator as 99.99999 or 100, bt is there any better denominator than this?
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  2. #2
    Flow Master
    mr fantastic's Avatar
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    Quote Originally Posted by Mukilab View Post
    A delivery lorry covers its outward journey at 50mph.


    It returns, over exactly the same distance at 33.3333mph.


    What is the lorry’s average speed over the entire journey?





    Not allowed to use a calculator. I would place the common denominator as 99.99999 or 100, bt is there any better denominator than this?
    t = \frac{x}{50} + \frac{x}{33 \frac{1}{3}} = \frac{x}{50} + \frac{3x}{100} = \frac{5x}{100} = \frac{x}{20}.

    Now do exactly what you have been shown in another thread.
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  3. #3
    Senior Member Mukilab's Avatar
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    Done.
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