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# S1 - Finding median of grouped data

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1. I'm struggling to find the median of grouped data in a table.

I know that you need to find the median position. The problem I'm having is that one source tells me that to find the median position you need to do n/2, but another source - and an exam question that I tried - I need to do (n+1)/2. And then another source says you need to draw a cumulative frequency graph to find it.

I'm just confused. (n+1)/2 worked in the exam question, but I'm not sure why it didn't work on MyMaths example questions. Does it vary?
2. (Original post by JordanL_)
Does it vary?
Yep. And markschemes should usually accept different versions. I would stick with (n+1)/2 if I were you, though.
3. (Original post by Zacken)
Yep. And markschemes should usually accept different versions. I would stick with (n+1)/2 if I were you, though.
Oh, that's annoying Thanks for the response. The mark scheme for this question I'm looking at only accepts (n+1)/2. Is there a way to know which one is right, or is it just random?
4. I've had this same problem! Stick with (n+1/2)
5. (Original post by Zacken)
Yep. And markschemes should usually accept different versions. I would stick with (n+1)/2 if I were you, though.
Just a quick question. When the number of terms are even. Do you do the middle of the two terms, so usually .5 or do you round it up? So it would be the second middle term. Does it matter?
I always thought that you just did the middle of the two terms, but my teacher taught it so you rounded it up.
6. (Original post by JordanL_)
Oh, that's annoying Thanks for the response. The mark scheme for this question I'm looking at only accepts (n+1)/2. Is there a way to know which one is right, or is it just random?
Are you sure the markscheme only accepts that answer? I've always used this and got it right all the time.
7. (Original post by Kholmes1)
Just a quick question. When the number of terms are even. Do you do the middle of the two terms, so usually .5 or do you round it up? So it would be the second middle term. Does it matter?
I always thought that you just did the middle of the two terms, but my teacher taught it so you rounded it up.
Middle of two terms, afaik.
8. (Original post by Zacken)
Are you sure the markscheme only accepts that answer? I've always used this and got it right all the time.
Yep, from the mark scheme:

SC2 for use of 50th value leading toEst = 140 + (25 /29 × 5) = 144.3(SC1 if over-specified)

Only get full marks for using the 50.5th value. What exam board are you on? It might be different for different boards?
9. (Original post by JordanL_)
Yep, from the mark scheme:

SC2 for use of 50th value leading toEst = 140 + (25 /29 × 5) = 144.3(SC1 if over-specified)

Only get full marks for using the 50.5th value. What exam board are you on? It might be different for different boards?
Edexcel, you?
10. (Original post by Zacken)
Edexcel, you?
MEI. I'll email my teacher and ask about it. Thanks for the help!
11. (Original post by JordanL_)
MEI. I'll email my teacher and ask about it. Thanks for the help!
Ah, yeah - I can see MEI being fussy about that sort of thing. Your teacher will be your best call here, I can't be of much assistance, sorry.
12. I'm doing MEI and I believe we are not required to find the median if the data is grouped (unless we get given (or asked to draw) a cumulative frequency graph, where 'n/2' is used to find the median). Whenever you have to find a median which is not from a cumulative frequency graph you must take the '(n+1)/2' th value as the median.

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