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

    18
    ReputationRep:
    (Original post by Notnek)
    Sorry I read your table wrong - I actually get 12.58. Your answer is not right. Can you please post your working in full?
    I’ve got 196 now by doing root 8486500-220 x (3590/220)/219
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    I’ve got 196 now by doing root 8486500-220 x (3590/220)/219
    I don't understand your working. What formula are you using?
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    I don't understand your working. What formula are you using?
    The one in the formula booklet (probably the wrong one) and I might be putting the wrong numbers for the wrong thing such as X
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    The one in the formula booklet (probably the wrong one) and I might be putting the wrong numbers for the wrong thing such as X
    If possible, can you please upload a screenshot of the formula you are looking at?
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    If possible, can you please upload a screenshot of the formula you are looking at?
    Name:  9639CB91-6238-4C7E-8FC4-F6D6CCD8878B.jpg.jpeg
Views: 4
Size:  21.0 KB
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    Name:  9639CB91-6238-4C7E-8FC4-F6D6CCD8878B.jpg.jpeg
Views: 4
Size:  21.0 KB
    You seem to be getting mixed up with your formulas. In your working you have a table which includes e.g. f x MP. Where did this table come from? Are you following an example? Did your teacher give you a formula?

    If you have time I recommend this video. It will explain the two main formulas.
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    You seem to be getting mixed up with your formulas. In your working you have a table which includes e.g. f x MP. Where did this table come from? Are you following an example? Did your teacher give you a formula?

    If you have time I recommend this video. It will explain the two main formulas.
    Ik they should be called Xi and that but I just put midpoint on that. I’m aware of that formula and the other 2 but not sure how to fill it
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    Ik they should be called Xi and that but I just put midpoint on that. I’m aware of that formula and the other 2 but not sure how to fill it
    I think you should start again and use this since your table indicates that you were trying to use this formula:

    \displaystyle \sigma^2 = \frac{\text{sum of frequency x midpoints}^2}{\text{sum of frequencies}}- \left(\frac{\text{sum of frequency x midpoints}}{\text{sum of frequencies}}\right)^2

    Firstly your fMP^2 column is wrong. fMP^2 means f\times MP^2 so you need to square the midpoint then multiply the result by the frequency.

    So can you please fix your table then post a screenshot?

    It seems like you will need to ask your teacher to clarify this topic to you.
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    I think you should start again and use this since your table indicates that you were trying to use this formula:

    \displaystyle \sigma^2 = \frac{\text{sum of frequency x midpoints}^2}{\text{sum of frequencies}}- \left(\frac{\text{sum of frequency x midpoints}}{\text{sum of frequencies}}\right)^2

    Firstly your fMP^2 column is wrong. fMP^2 means f\times MP^2 so you need to square the midpoint then multiply the result by the frequency.

    So can you please fix your table then post a screenshot?

    It seems like you will need to ask your teacher to clarify this topic to you.
    The whole class performed poorly on this topic so she’s going over it but wants us to fix the 3 questions in the test before the lesson. I’ll get back to you I think I’m getting closer
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    The whole class performed poorly on this topic so she’s going over it but wants us to fix the 3 questions in the test before the lesson. I’ll get back to you I think I’m getting closer
    Okay great. I'm sorry if my earlier posts confused you - I wasn't sure what you knew/didn't know. Plus helping with stats questions on TSR is quite new for me
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    Okay great. I'm sorry if my earlier posts confused you - I wasn't sure what you knew/didn't know. Plus helping with stats questions on TSR is quite new for me
    Would you mind showing your working so I can learn to be able to do the next few? I’ve been doing this for like 1h now and I’m even getting maths error now
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    Would you mind showing your working so I can learn to be able to do the next few? I’ve been doing this for like 1h now and I’m even getting maths error now
    Sorry I don't have time to write out a solution but I can guide you through this one.

    Your fMP^2 column is wrong. So for the first entry of that column you need to do 80\times 2.5^2 = 500 so 500 is the frst entry instead of 40000. Can you fix the rest of them then work out the total and post your working?
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    Sorry I don't have time to write out a solution but I can guide you through this one.

    Your fMP^2 column is wrong. So for the first entry of that column you need to do 80\times 2.5^2 = 500 so 500 is the frst entry instead of 40000. Can you fix the rest of them then work out the total and post your working?
    We were told to do f x mp then square answer. As you can see it makes a big difference
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    We were told to do f x mp then square answer. As you can see it makes a big difference
    Can you please explain in words how you were taught to do all this? It doesn't matter if what you say is wrong.

    I don't want to give you a method that is different to your teachers. If you want to use a method that I suggest then let me know.
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    Can you please explain in words how you were taught to do all this? It doesn't matter if what you say is wrong.

    I don't want to give you a method that is different to your teachers. If you want to use a method that I suggest then let me know.
    Thanks for all your help but I think I’m going to have to give up
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    Thanks for all your help but I think I’m going to have to give up
    I'll post a solution for your question. Give me a few mins.
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    Thanks for all your help but I think I’m going to have to give up


    \displaystyle \sigma^2 = \frac{\sum fx^2} {\sum f}- \left(\frac{\sum fx}{\sum f}\right)^2

    Spoiler:
    Show
    =\displaystyle \frac{93425}{220} - \left( \frac{3590}{220}\right)^2 = 158.376...

    So \sigma = \sqrt{158.376...} = 12.58


    (For anyone wondering, full solutions are not normally allowed unless a thread has gone on for a while and the OP is still stuck.)
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)


    \displaystyle \sigma^2 = \frac{\sum fx^2} {\sum f}- \left(\frac{\sum fx}{\sum f}\right)^2

    =\displaystyle \frac{93425}{220} - \left( \frac{3590}{220}\right)^2 = 158.376...

    So \sigma = \sqrt{158.376...} = 12.58
    Ok so I have that apart from the column on the right because we’ve definitely been told to square the answer of fx not f x x^2
    Posted on the TSR App. Download from Apple or Google Play
    • TSR Support Team
    • Study Helper
    Offline

    20
    ReputationRep:
    (Original post by Reece.W.J)
    Ok so I have that apart from the column on the right because we’ve definitely been told to square the answer of fx not f x x^2
    I've shown you a method that will give you the answer. If your teacher is using a different method then please check with them.
    • Thread Starter
    Offline

    18
    ReputationRep:
    (Original post by Notnek)
    I've shown you a method that will give you the answer. If your teacher is using a different method then please check with them.
    Ok thanks so much for your help
    Posted on the TSR App. Download from Apple or Google Play
 
 
 
  • 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
    Did TEF Bronze Award affect your UCAS choices?
    Useful resources

    Make your revision easier

    Maths

    Maths Forum posting guidelines

    Not sure where to post? Read the updated guidelines here

    Equations

    How to use LaTex

    Writing equations the easy way

    Student revising

    Study habits of A* students

    Top tips from students who have already aced their exams

    Study Planner

    Create your own Study Planner

    Never miss a deadline again

    Polling station sign

    Thinking about a maths degree?

    Chat with other maths applicants

    Can you help? Study help unanswered threads

    Groups associated with this forum:

    View associated groups
  • 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.