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This isn't homework, I am boggling my head over it though.

I got all sorts of answers, just not the answer my book demands.

For what value of $x$ the mean of the given observations $2x - 5, x + 3, 7 - x, 5-x$ and $x + 9$ with frequencies $2,3,4,6$ and $1$ respectively is $4$?

I seriously cant solve this, help would be MUCH appreciated. Note: Please don't use any advanced statistics formula, we are still on the basics. Sum of $f_ix_i$ over sum of $f_i$ is all I can use.

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    I think theres some sort of mistake in the book, mathematica doesnt give the right answer either :/ Answer accepted however2012-09-11

1 Answers 1

5

Hint: $\text{mean = }\frac{\sum_{i=1}^n f_ix_i}{\sum_{i=1}^n f_i}$ where $f_i$ is the frequency of $x_i$ event.

$\frac{2(2x-5) + 3(x+3) + 4(7-x) +6(5-x) + (x+9)}{16}=4$ $4x-10+3x+9+28-4x+30-6x+x+9=64$ $-2x+66=64$ $x=1$

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    Found a tiny mistake. In your solution you marked the final one(x + 9) as (x - 9)2012-09-10