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Math Help - test question

  1. #1
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    test question

    I had a Stats test today. Heres a question i was wondering about..see if im right..I cant remember the exact words, but you will get the basic idea.

    Theres a class.
    Then the said the percentages for left handed girls, left handed boys, right handed girls, right handed boys. They had a table like this..

    Left Right
    Boy X X #

    Girl X X #
    # # #

    Where I have a #...they had a percentage
    Where I have an X...there was nothing there.

    So they say that the left handed girl is independent of left hands...i think thats what they said.
    Question: How many left handed girls are there?
    Multiple choice...they were like 2 5 7 10 and cant define

    Would it be cant define? Cus they are independent?
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  2. #2
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    If they didn't tell you the total number of people in the class (only the percentages of each type; left and right handed) then you cannot determine how many of each there are. There could be any number since the class could be any size.

    And did they say "being left handed is independent of gender"? Please explain the table you were given more clearly. As you have explained it appears that you have 3 columns and 3 rows of data, but only 4 categories (left-girl, right-girl, left-boy, right-boy).
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  3. #3
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    yes theres 4 categories

    Heres an example...not exactly what the # were.


    ........ Left....Right
    Boy...................15

    Girl ...................22
    ........20 .......1737


    they actually gave a number..not percentages..
    Last edited by Morgan82; March 25th 2008 at 03:03 PM. Reason: Trying to make the table better
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  4. #4
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    Ah I see:

    there are 15 boys in the class and 22 girls,
    there are 20 lefties in the class and 17 righties.
    so 37 total students.

    n left handed girls leads to the table:

    <br />
\begin{array}{cccc}<br />
 \text{ } & left & right & total \\<br />
       boys &  20-n & 15-(20-n) &15 \\<br />
girls &  n & 22-n & 22\\<br />
total & 20 & 17 & 37 \end{array} <br />

    Well there cannot be 2 left handed girls, since then there are more left handed boys than there are boys which is obviously not possible. There must be at least 5 left handed girls. But there could be 6 or 7 or even 8 left handed girls, you don't know. It might be possible to gives totals that force the number of left handed girls to be one and only one number but with the totals provided the number of left handed girls could be a range of different values.
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