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Math Help - Mean of a Set of Numbers

  1. #1
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    Mean of a Set of Numbers

    Hello. I recently encountered this question on a math test, and it totally stumped me.

    The mean of a set of numbers is 0.40. The sum of the numbers is 56. How many numbers are in the set?

    I guessed 14 (completely random guess). The correct answer turned out to be 140. It was a multiple choice question, but I forgot what the other two choices were.

    I know that when somebody tells me how to figure it out, it'll seem really dumb and obvious, but I just can't see how to right now. It's the only question on the test that I had no idea how to solve. Any help that anyone could give me would be greatly appreciated!
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by greenstupor View Post
    Hello. I recently encountered this question on a math test, and it totally stumped me.

    The mean of a set of numbers is 0.40. The sum of the numbers is 56. How many numbers are in the set?

    I guessed 14 (completely random guess). The correct answer turned out to be 140. It was a multiple choice question, but I forgot what the other two choices were.

    I know that when somebody tells me how to figure it out, it'll seem really dumb and obvious, but I just can't see how to right now. It's the only question on the test that I had no idea how to solve. Any help that anyone could give me would be greatly appreciated!
    How do we find the mean?

    For a given set of numbers,

    \mbox {mean} = \frac { \mbox {sum of the numbers } }{ \mbox {the number of numbers we have} }

    \Rightarrow \mbox { the number of numbers there are } = \frac { \mbox { sum of the numbers} }{ \mbox {mean } }


    So here, \mbox {the number of numbers there are } = \frac {56}{0.4} = 140
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  3. #3
    Member Jonboy's Avatar
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    That's totally amazing. I never thought of such a brilliant method.
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    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by Jonboy View Post
    That's totally amazing. I never thought of such a brilliant method.
    Hmmm, "brilliant" huh? well, i guess, maybe. I didn't think it was that big o' deal, all i did was transpose the formula for the mean
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  5. #5
    Member Jonboy's Avatar
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    Quote Originally Posted by Jhevon View Post
    Hmmm, "brilliant" huh? well, i guess, maybe. I didn't think it was that big a deal, all i did was transpose the formula for the mean
    I've seen a problem like this on my ACT and I had not a clue to solve it. I would of never thought of writing out what the mean was and transposing it. That's neat.
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  6. #6
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    Quote Originally Posted by Jonboy View Post
    I've seen a problem like this on my ACT and I had not a clue to solve it. I would of never thought of writing out what the mean was and transposing it. That's neat.
    I totally agree. I never would've thought to do that on my own. Thanks so much for the help!
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