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    Hi, I know this is very stupid of me to ask but I wasnt taught when to do this, but I need some help...

    I know how to inrepolate and and find the values, I just never know when to add 1 onto the total number before I divide by 4 or 2 or whatever. It loses me a lot of marks and I'm wondering if anyone would like to explain.

    E.g.

    out of 200 values, find the median

    so do I do 200x2/4?
    or do I do (200+1)x2/4?

    I feel like an idiot, but its the only part I lose marks at!
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    Oh, and what about grouped data?
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    (Original post by i need ferrets)
    Hi, I know this is very stupid of me to ask but I wasn't taught when to do this, but I need some help...

    I know how to interpolate and and find the values, I just never know when to add 1 onto the total number before I divide by 4 or 2 or whatever. It loses me a lot of marks and I'm wondering if anyone would like to explain.

    E.g.

    out of 200 values, find the median

    so do I do 200x2/4?
    or do I do (200+1)x2/4?

    I feel like an idiot, but its the only part I lose marks at!
    This might well vary between 'exam boards'. You'd better check mark schemes or specifications....or just ask your teacher.
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    If you're interpolating, you do not need to use the +1 method. It is normally correct to just use n/2 which will give you some number, and find that term. This is generally more accurate.

    I also suggest checking with your teacher though because it might be different somehow for your board.
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    This is what we got taught:

    For non-grouped data (e.g stem and leaf)

    n/2, if it gives an answer to .5, round it up, if it gives a whole number, round it up to its .5,
    e.g
    10/2 = 5 => 5.5th value
    11/2 = 5.5 => 6th value.

    Same rule for 3n/4 (Q3)

    and n/4 (Q1)

    With grouped data, you do not do this rounding rule, the value you need would simply be n/2, etc.
 
 
 
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