You are Here: Home >< Maths

# Simple Variance Stats help needed! Watch

1. Hi, i'm stuck on an easy question

An automobile dealer calculates the proportion of new cars sold that have been returned variousnnumbers of times for the corrections of defects during the warranty period.

number of returns - 0, 1, 2, 3, 4
Proportion - 0.28, 0.36, 0.23, 0.09, 0.04

The question is to find the variance of the numbers of returns of an automobile for corrections for defects defects during warranty?

I found out the mean as 1.25 defects and did

[(0-1.25)^2+(1-1.25)^2+(2-1.25)^2+(3-1.25)^2+(3-1.25)^2+(4-1.25)^2] /5

this gives me 2.25 whereas the answer is 1.1675... any ideas would be greatly appreciated Much love in advanced.
2. (Original post by xela)
Hi, i'm stuck on an easy question

An automobile dealer calculates the proportion of new cars sold that have been returned variousnnumbers of times for the corrections of defects during the warranty period.

number of returns - 0, 1, 2, 3, 4
Proportion - 0.28, 0.36, 0.23, 0.09, 0.04

The question is to find the variance of the numbers of returns of an automobile for corrections for defects defects during warranty?

I found out the mean as 1.25 defects and did

[(0-1.25)^2+(1-1.25)^2+(2-1.25)^2+(3-1.25)^2+(3-1.25)^2+(4-1.25)^2] /5

this gives me 2.25 whereas the answer is 1.1675... any ideas would be greatly appreciated Much love in advanced.
Var(X)=E(X^2) - E(x) ^2

So add up x^2 *P(X=x) and subtract the square of the mean. Answer 467/400 = 1.1675 (as you said).
3. (Original post by Get me off the £\?%!^@ computer)
Var(X)=E(X^2) - E(x) ^2

So add up x^2 *P(X=x) and subtract the square of the mean. Answer 467/400 = 1.1675 (as you said).
Cheers for the reply but sorry I still don't get it could you show more working and explain it to a complete n00b, thanks.
4. There's an example here.

http://www.tutorvista.com/math/varia...andom-variable

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.

This forum is supported by:
Updated: November 30, 2010
Today on TSR

### Degrees to get rich!

... and the ones that won't

### Cambridge interviews pour in...

Discussions on TSR

• Latest
• ## 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
Useful resources

## Make your revision easier

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## 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

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