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Math Help - mean

  1. #1
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    mean

    The mean of a set of numbers is 20. If one number is increased by 360, the mean increased to 40. How many numbers are in the set?

    use no algebra.
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  2. #2
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    \frac{a_1+a_2+\dots +a_n}n+40=\frac{a_1+a_2+\dots +a_n+360}n \rightarrow 40=\frac {360}n\rightarrow \boxed{n=9}.
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  3. #3
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    I am not allowed to use any algebra.
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  4. #4
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    Quote Originally Posted by nancymcwilliams View Post
    The mean of a set of numbers is 20. If one number is increased by 360, the mean increased to 40. How many numbers are in the set?

    use no algebra.
    20 = \frac{\sum x_i}{n}

    40 = \frac{\left(\sum x_i\right) + 360}{n} = \frac{\sum x_i}{n} + \frac{360}{n} = 20 + \frac{360}{n}

    \Rightarrow 20 = \frac{360}{n} \Rightarrow n = 18.
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  5. #5
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    Quote Originally Posted by nancymcwilliams View Post
    I am not allowed to use any algebra.
    Then just give the answer of 18 and say it came to you in a dream.


    Fer cryin' out loud ...... I don't see how it can be done without some level of algebra being involved. Just say it's obvious that n = 360/20 - that way you're only using arithmetic.
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  6. #6
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    Reply

    You always use algebra anyway be it in word or math symbols. Just write down what the math symbols mean.
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