You are Here: Home >< Maths

# S2 - Choosing The Correct Approximation watch

1. The very last question on the June 2001 paper has a B(75, 0.08). As n is large and p is small, you could use the poisson distribution as an approximation, but as np >5 and np(1-p) > 5 you could use the normal distribution as an approximation.

Which one should I use? Why?

Many thanks.
2. (Original post by seankhn)
The very last question on the June 2001 paper has a B(75, 0.08). As n is large and p is small, you could use the poisson distribution as an approximation, but as np >5 and np(1-p) > 5 you could use the normal distribution as an approximation.

Which one should I use? Why?

Many thanks.
You would use the poisson, because n is large and p is small, normal would be used when the distribution is fairly symmetrical and p is large
3. Only use the normal when p is large?

What if it were B(750, 0.08)?

Surely a normal approximation would be a better idea than Po(60)?
4. (Original post by seankhn)
Only use the normal when p is large?

What if it were B(750, 0.08)?

Surely a normal approximation would be a better idea than Po(60)?
yeh, use normal, cos poisson tables dont go that high - i just multiply stuff and if can't use one thing, use the other - process of elimination

pk
5. You always try to use the Poisson for the Binomial approximation because both are discrete and so its more accurate. Only use the normal when the poisson can't be used (i.e when np > 10)
6. Thanks folks.

### 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: June 18, 2005
The home of Results and Clearing

### 2,504

people online now

### 1,567,000

students helped last year
Today on TSR

### University open days

1. Keele University
Sun, 19 Aug '18
2. University of Melbourne
Sun, 19 Aug '18
3. Sheffield Hallam University
Tue, 21 Aug '18
Poll
Useful resources

### 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