s1 urgennnnnt help

guys please can someone help my exam is soo close --

so if we get the position of the median in the stem diagram is the 2.25th value do we take the 2nd or the 3rd value or their mean .. same for 2.75???

also for 2.5??????????? i thought we always round up even for 2.25 but i was just solving a question and the position was 16.5 and it took the mean of the 16th and 17th value! please can someone explain the three cases im very very confused on which to doooo

For a stem and leaf diagram, it's continuous, grouped data. For these type of data, finding the position of the median is achieved using the formula n/2.

If n = odd number, the position of your median will be, say 16.5.
To find the 16.5th value in a stem and leaf diagram, count along to the 16th and 17th values and take the average of the two -- (add the two numbers together and divide by two; in other words, the midpoint).
This is your median.

I don't think I've answered your other questions (if, indeed, I answered any), but I don't think that a stem and leaf diagram can have a median position of 2.25 or any other x.25 (where x is an integer). In any case, I've never seen a median of x.25 in any past paper question for S1.

Hope this helped!!

the pastpapers use n+1 /2!!!!!!!!! im totally sure about this

Yep. That was a BIG mistake by me. Just looked over my past papers and I was wrong... stem and leaf is discrete which is therefore why you use the formula n+1/2 (just as you said)...

(in fact, Q1 of June 2014 - EDEXCEL is about a median in a stem and leaf)

Sorry for the confusion I may have caused

no problem! at least i am sure now .. anyway so lets assume that i get a postion of median being 2.25 / 2.5/2.75!! wth do i doooooooooo

Hmmmmm...

For 2.5 as the position, (I suspect you know this but) take the mean between the second and third values.

How would you get a position of 2.25 or 2.75 on a stem and leaf diagram?? Have you got an example??

yeah for example our total values are are 16.. and we want to find the two quartiles we'd get positions of 4.25 and 4.75!

Okaaay...

So, you have found your median.
The position of the median is the 8.5th value.

Divide the stem and leaf in half...
I would actively draw a boundary between the 8th and the 9th value.

You now have 8 values on one side and 8 values on the other.

To find the lower quartile, treat the lower half of the ENTIRE stem and leaf diagram as being separate. Locate the position of the median using your new "only 8 values" diagram. Here, the position of the median is the 4.5th value (take the mean of the 4th and 5th).

For the upper quartile, use the second, upper half of the ENTIRE stem and leaf (this ranges from the 9th value to the 16th (final) value). Again, the median of this upper half is the 4.5th value... do the same as before.

^^ Dunno if anything I said above makes sense or is correct (but I think it works)

omg omg okay great! thanks so much honestly.. lets say the position of the median was 8 .. when we are dividing the diagram we only take the first 7 values for the new set of values right??!!