Turn on thread page Beta
 You are Here: Home >< Maths

# S1: Central limit theorem question watch

1. I would like to know if my method is correct for 6(b). I'm fine with 6(a).

I did a quick sketch and realised that I have an area of 0.6 'at the right' of the normal distribution. Therefore, the value of z I need would be obtained by using the value of p=0.4.

Using the curve symmetry, the z value at 0.4 would be the same as the z value at 0.6, but negative. Using Table 4 of the AQA formula book, it is -0.2533.

I then plug this and the values given into the z-score standardisation formula (the one for the sample mean distribution), and rearranged to find an x of 19.4934.

...

Is there a better approach that is more intuitive? It seems you could only do it this way by carefully looking at sketches you make. I'm not sure if my working is even correct despite getting the correct answer.
2. (Original post by W. A. Mozart)
I would like to know if my method is correct for 6(b). I'm fine with 6(a).

I did a quick sketch and realised that I have an area of 0.6 'at the right' of the normal distribution. Therefore, the value of z I need would be obtained by using the value of p=0.4.

Using the curve symmetry, the z value at 0.4 would be the same as the z value at 0.6, but negative. Using Table 4 of the AQA formula book, it is -0.2533.

I then plug this and the values given into the z-score standardisation formula (the one for the sample mean distribution), and rearranged to find an x of 19.4934.

...

Is there a better approach that is more intuitive? It seems you could only do it this way by carefully looking at sketches you make. I'm not sure if my working is even correct despite getting the correct answer.
That appears to be the appropriate method - not sure about AQA in particular but it helps to be familiar with the sketch of the normal distribution and how the z values are related.

Turn on thread page Beta

### Related university courses

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: October 29, 2017
Today on TSR

### He lied about his age

Thought he was 19... really he's 14

### University open days

1. University of Bradford
Wed, 25 Jul '18
2. University of Buckingham
Psychology Taster Tutorial Undergraduate
Wed, 25 Jul '18
3. Bournemouth University
Clearing Campus Visit Undergraduate
Wed, 1 Aug '18
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

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