Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    16
    ReputationRep:
    Hi - I have one small problem question on the Jan 15 S2 paper I require a bit of help with!

    https://57a324a1a586c5508d2813730734...%20Edexcel.pdf

    There's a link to the paper..

    It is 6 (d) and the entirety of Q7 I am struggling with - mainly with Q7 I can't understand how it is y is normally distributed with (n/5, 4n/25)???

    Thanks!
    Offline

    12
    ReputationRep:
    no matter how many questions there are, guessing randomly you're gonna get 1 out of 5 questions right
    let n =number of correct questions
    the mean number of correctly guessed questions would then b n/5
    variance is just the mean*(1-probabilty of success) so n/5 multiplied by (1-0.2) =4n/25
    • Thread Starter
    Offline

    16
    ReputationRep:
    (Original post by cheesedrew)
    no matter how many questions there are, guessing randomly you're gonna get 1 out of 5 questions right
    let n =number of correct questions
    the mean number of correctly guessed questions would then b n/5
    variance is just the mean*(1-probabilty of success) so n/5 multiplied by (1-0.2) =4n/25
    Ahhhhh... thank you!
    Offline

    22
    ReputationRep:
    I think it is better put as you having n trials and p = 1/5.

    So variance of the binomial is given by np(1-p).
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: June 3, 2016
Poll
Do you agree with the proposed ban on plastic straws and cotton buds?
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

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

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