# Homework Help: Binomial distribution formulae?

1. Aug 27, 2009

### morr485

1. Let the p.m.f. pf M be defined by f(m)=x/8, x=1,3,4. What is the mean of M?

2. n!/n-r*p^n*(1-p)^n-r

3. 3!*1/3^3*2/3^2=.59 This is not the correct answer!

Last edited: Aug 28, 2009
2. Aug 28, 2009

### D H

Staff Emeritus
Re: p.m.f.

That isn't the correct answer because you aren't using the correct expression for calculating the mean. Why are you using the binomial distribution formulae?

3. Aug 28, 2009

### morr485

Re: p.m.f.

D.H.

What distribution of equation should I use? I'm from the behavioral sciences and I
am not familiar with this problem.

4. Aug 28, 2009

### HallsofIvy

Re: p.m.f.

The problem tells you what to use! The probability is given by f(m)=x/8, x=1,3,4. That is, f(1)= 1/8, f(3)= 3/8 and f(4)= 4/8= 1/2. And the mean is given by [itex]\sum x f(8)[itex].