# Expressions for Binomial Distributions

• Oct 18th 2009, 06:15 AM
davidrocastle
Expressions for Binomial Distributions
Hi i am working on a Binomial Distribution

If i know the Mean of A is 7.6

and

I know the Variance of A is 5.48

How do you write an expression that A >= 28?
• Oct 18th 2009, 06:19 AM
CaptainBlack
Quote:

Originally Posted by davidrocastle
Hi i am working on a Binomial Distribution

If i know the Mean of A is 7.6

and

I know the Variance of A is 5.48

How do you write an expression that A >= 28?

Mean = Np

Variance =Np(1-p)

so (1-p)=5.48/7.6 etc...

CB
• Oct 18th 2009, 06:54 AM
davidrocastle
So as the question is put chances of having a work accident is on a weekday is .2 and weekend is .3

A is random variable representing no. of accidents in february

mean of A is 7.6
variance of A is 5.48

for P(<=28)= 1-P(>=27) = 1-Bin(27,?,?.....

Am i on the right path here?
• Oct 18th 2009, 07:16 AM
CaptainBlack
Quote:

Originally Posted by davidrocastle
So as the question is put chances of having a work accident is on a weekday is .2 and weekend is .3

A is random variable representing no. of accidents in february

mean of A is 7.6
variance of A is 5.48

for P(<=28)= 1-P(>=27) = 1-Bin(27,?,?.....

Am i on the right path here?

More or less but first work out the valuse of p and N.

However you said earlier that you want p(A>=28)=1-p(A<=27).

Also please calculate N, then think again about what the question is asking. Also check for typos.

CB
• Oct 18th 2009, 07:48 AM
davidrocastle
Sorry again i am a bit lost,

what i was looking for is write an expression for probability that A>= 28

How do i calculate N?