Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    8
    ReputationRep:
    Can anyone explain how to work quartiles (median, lower quartile and upper quartile)?

    For example how is the process different for discrete and continuous data?
    When to use n and when to use n+1?
    When to round, not round, or find the midpoint between two values?
    Offline

    2
    ReputationRep:
    (Original post by GarlicBread01)
    Can anyone explain how to work quartiles (median, lower quartile and upper quartile)?

    For example how is the process different for discrete and continuous data?
    When to use n and when to use n+1?
    When to round, not round, or find the midpoint between two values?
    For discrete you can use n/2 for median. If it is not a whole number round up. If it is a whole number then the median would be midway between this turn and the term above it. This is the same for quartiles. There is no rule having to use n/2 and n+1\2, you can use either. It is just that there is a different rule for n+1/2 when the answer is a whole number (you may aswell just learn how to use the n/2 and forget about the other or vise versa.

    For contiuous data you just use n/2 and don't round and use interpolation to find the median and quartiles.
    Offline

    18
    ReputationRep:
    So this is the first time I've come across a question like this! Can someone please explain it to me?...
    Click to enlarge...
    Name:  S1 June 2014 Q2.png
Views: 234
Size:  30.0 KB
    Offline

    3
    ReputationRep:
    (Original post by Philip-flop)
    So this is the first time I've come across a question like this! Can someone please explain it to me?...
    Click to enlarge...
    Name:  S1 June 2014 Q2.png
Views: 234
Size:  30.0 KB
    Just put the values of y into the equation and solve for x
    so
    60.8=1.4x-20
    x=60.8+20/1.4=57.7

    then do the same for s.d but remember that the -20 doesn't have an effect on it.

    If you're still confused I suggest you look on exam solutions he explains it well.
    Offline

    11
    ReputationRep:
    I hope we don't get a paper like the June 2015 otherwise I'm failing. Every other paper has been good for me except the 2015 which I scored terribly in 😐
    Offline

    2
    ReputationRep:
    (Original post by siamesedaffodil)
    sd is affected by only multiplication/division
    mean is affected by multiplication, division, addition and subtraction

    standard deviation measures how spread out data is from the mean.

    logically, if you added 10 to each piece of data, the standard deviation would stay the same as each point would move 10 places and the distance between them would stay the same. so standard deviation is not affected by addition/subtraction. however, standard deviation IS affected by multiplication/division. Think of transforming graphs-- when you add or subtract 2 from a graph, all points move 2 places. if you multiplied a graph by 2, the graph is stretched and the distance between each point has changed. in the same way, standard deviation is affected by multiplication/division

    as for the mean...it is a measure of location and is affected by ALL coding.
    Thankyou so much!
    Offline

    13
    ReputationRep:
    (Original post by GarlicBread01)
    Can anyone explain how to work quartiles (median, lower quartile and upper quartile)?

    For example how is the process different for discrete and continuous data?
    When to use n and when to use n+1?
    When to round, not round, or find the midpoint between two values?
    Quote I found. Also find this tricky. Would like if someone could confirm this?

    (Original post by Lou Reed)
    For the new Edexcel syllabus...For Continuous data (grouped frequency tables, histograms etc.)

    Median:n/2 and use linear interpolation

    Quartiles:n/4 or 3n/4 and use linear interpolation

    Linear Interpolation:m + cw[(X-fc)/f]where m = minimum boundary of the class that X is incw = class width of the class that X is inX = n/2 for median, n/4 for lower quartile, 3n/4 for upper quartilen = total number in the samplefc = cumulative frequency of the classes below the class that X is inf = frequency of the class that X is in

    For Discrete data (stem and leaf, listed data etc, frequency tables)

    Median: (n+1)/2 and pick that value, if it is a .5 then take average of the two values above and below it (e.g. if (n+1)/2 = 50 then pick the 50th value, if (n+1)/2 = 50.5 then average the 50th and 51st values)

    Quartiles:n/4 or 3n/4 and round UP and pick that value. If n/4 or 3n/4 is an integer, then take average of that value and the one above it (e.g. if n/4 = 25, then take average of 25th and 26th values).
    Offline

    0
    ReputationRep:
    (Original post by hogree)
    Quote I found. Also find this tricky. Would like if someone could confirm this?
    Best way:

    Never use n+1. LQ n+1/4 Median n/2 and UQ 3n/4

    Discrete data, if you get an integer then your answer is the average of this number and the one above, if it is a decimal answer then you round up to the next number.

    Example - 10 terms. LQ = 10/4 = 2.5 = 3rd number, 10/2 = 5 = average of 5th and 6th number. 10/4*3 = 7.5 = 8th number.

    Continuous data LQ n+1/4 Median n/2 and UQ 3n/4 then interpolate
    Offline

    0
    ReputationRep:
    (Original post by wkaren)
    Best way:



    Never use n+1. LQ n+1/4 Median n/2 and UQ 3n/4

    Discrete data, if you get an integer then your answer is the average of this number and the one above, if it is a decimal answer then you round up to the next number.

    Example - 10 terms. LQ = 10/4 = 2.5 = 3rd number, 10/2 = 5 = average of 5th and 6th number. 10/4*3 = 7.5 = 8th number.

    Continuous data LQ n+1/4 Median n/2 and UQ 3n/4 then interpolate
    Sorry first line should say:

    Never use n+1. LQ n/4 Median n/2 and UQ 3n/4
    Offline

    13
    ReputationRep:
    (Original post by wkaren)
    Sorry first line should say:

    Never use n+1. LQ n/4 Median n/2 and UQ 3n/4
    Makes sense. Thanks for clearing that up.
    Offline

    19
    ReputationRep:
    (Original post by physicsamor)
    I hope we don't get a paper like the June 2015 otherwise I'm failing. Every other paper has been good for me except the 2015 which I scored terribly in 😐
    What made you do badly on June 2015 paper?
    Offline

    11
    ReputationRep:
    (Original post by kkboyk)
    What made you do badly on June 2015 paper?
    I feel like just giving up with S1, that paper gave me a panic attack. It was question 5 and question 6 and a mistake with the venn diagram (but at least I understand where i went wrong)

    Especially with question 6 iii and 6 iiv and 6B
    And just 5 in general (but more of the wording) I've tried looking at Ma, ms and videos but I just couldn't understand.

    Oh well.
    Offline

    18
    ReputationRep:
    Why is it with Edexcel past papers (including C1, C2, S1 etc) they progressively get more difficult each year? e.g. June 2007 is so much easier in comparison to June 2015!!
    Offline

    11
    ReputationRep:
    (Original post by Philip-flop)
    Why is it with Edexcel past papers (including C1, C2, S1 etc) they progressively get more difficult each year? e.g. June 2007 is so much easier in comparison to June 2015!!
    It's annoying, they want me to fail
    Offline

    9
    ReputationRep:
    Quick question, if for my answer i have given the correct answer then underneath I have written the answer to 3.s.f wrongly. would I get the A1 for my first answer as the mark scheme states answers which round to that or would they see my incorrect answer after my correct answer and lose the mark. basically do they ignore subsequent marking once you get your answer?
    Offline

    2
    ReputationRep:
    How confident are you guys with s1?
    I feel as if I'm going to mess this up.

    Posted from TSR Mobile
    Offline

    9
    ReputationRep:
    (Original post by T17MA)
    How confident are you guys with s1?
    I feel as if I'm going to mess this up.

    Posted from TSR Mobile
    same, i keep making the same mistakes even tho i have enough time to check my questions three times over
    Offline

    16
    ReputationRep:
    I'm really bad at probability. Really bad. Any tips?
    Offline

    19
    ReputationRep:
    (Original post by LittleBoxes)
    I'm really bad at probability. Really bad. Any tips?
    Watch these tutorial videos (or go through your textbook again, and if struggling keep asking questions here or to your teacher), and do the Probability past paper question booklet from Physics and Maths Tutor.

    (Original post by T17MA)
    How confident are you guys with s1?
    I feel as if I'm going to mess this up.

    Posted from TSR Mobile
    Feel a bit meh. I need to get more than 90% and I don't really have the motivation. S1 is too boring and very wordy.

    (Original post by physicsamor)
    I feel like just giving up with S1, that paper gave me a panic attack. It was question 5 and question 6 and a mistake with the venn diagram (but at least I understand where i went wrong)

    Especially with question 6 iii and 6 iiv and 6B
    And just 5 in general (but more of the wording) I've tried looking at Ma, ms and videos but I just couldn't understand.

    Oh well.
    I struggled with the very same questions when I was doing it as a mock on Friday. Keep practicing in these particular questions to make you feel more confident.
    Offline

    2
    ReputationRep:
    can someone explain to me question 3e:

    https://1a388b28f5ce9318f837a64962fc...%20Edexcel.pdf

    Thank you
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    What's your favourite Christmas sweets?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.