Hey! Sign in to get help with your study questionsNew here? Join for free to post

Bournelli, equation for variance? (with picture!)

Announcements Posted on
Find the answers: Edexcel GCSE maths unofficial mark scheme 05-05-2016
  1. Offline

    ReputationRep:
    So I was watching khan academy videos on Stats, and I noticed this:

    why he does not calculate the variance of the sample he has first, and then approximate the variance of the normal distribution using the result?

    Rest of the question is on picture in white text, any help much appreciated
    Attached Thumbnails
    Click image for larger version. 

Name:	Xu5ff.jpg 
Views:	31 
Size:	66.0 KB 
ID:	148943  
  2. Offline

    ReputationRep:
    Please help, exam tomorrow :/
  3. Offline

    ReputationRep:
    What is M_1 (or mu_1) at the very start? And what is he trying to show, the normal distribution approximation for the sum of 1000 choices of 0 or 1 where the probability of choosing 1 is 0.642? In any case, that's a freaking tiny variance that can't be right for whatever
  4. Offline

    ReputationRep:
    (Original post by Hopple)
    What is M_1 (or mu_1) at the very start? And what is he trying to show, the normal distribution approximation for the sum of 1000 choices of 0 or 1 where the probability of choosing 1 is 0.642? In any case, that's a freaking tiny variance that can't be right for whatever
    mu_1 is mean of sample number 1

    He tries to show how many people have voted for a candidate (choice 1) and how many didn't (choice 0), by using this sample he then creates a normal distribution of all the sample means.
  5. Offline

    ReputationRep:
    (Original post by Moa)
    mu_1 is mean of sample number 1

    He tries to show how many people have voted for a candidate (choice 1) and how many didn't (choice 0), by using this sample he then creates a normal distribution of all the sample means.
    I'm still not sure what he's trying to show, that final super tiny variance makes no sense to me, sorry. Was there anything prior to this question he built upon?
  6. Offline

    ReputationRep:
    (Original post by Hopple)
    I'm still not sure what he's trying to show, that final super tiny variance makes no sense to me, sorry. Was there anything prior to this question he built upon?
    Maybe the video can help you, if you have time to skim through it:

    http://www.youtube.com/watch?v=a1Ye5...28115D3D8A2566
  7. Offline

    ReputationRep:
    (Original post by Moa)
    Maybe the video can help you, if you have time to skim through it:

    http://www.youtube.com/watch?v=a1Ye5...28115D3D8A2566
    Ah, I see. It builds on earlier videos (or so he says), but he's working out how the sample mean varies. He has worked out the variance of the first sample, but by a 'stock' formula (Bin(n,p) has variance np(1-p)), which gives the same answer as your more general formula. I'm assuming you're okay with the rest, just the calculation of the variance was different to what you expected?
  8. Offline

    ReputationRep:
    (Original post by Hopple)
    Ah, I see. It builds on earlier videos (or so he says), but he's working out how the sample mean varies. He has worked out the variance of the first sample, but by a 'stock' formula (Bin(n,p) has variance np(1-p)), which gives the same answer as your more general formula. I'm assuming you're okay with the rest, just the calculation of the variance was different to what you expected?
    Yes that is it, its all clear now, I can see that the results of "mine" and his formulas are very close.

Reply

Submit reply

Register

Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. Oops, you need to agree to our Ts&Cs to register
  2. Slide to join now Processing…

Updated: May 18, 2012
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Today on TSR

Edexcel GCSE maths answers

Check the unofficial mark scheme

Poll
What date is the EU referendum on?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read here first

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