Help Needed on Stats Q

[leafsrock]

Hi,

I'm having a really hard time solving this question. Any help would be greatly appreciated.

"Airborne spores produce tiny mould colonies on gelatin plates in a laboratory. The many plates average 3 colonies per plate. What fraction of plates contains exactly 3 colonies? If the average number of colonies is some large integer m, what fraction of plates contains exactly m colonies?"

Thanks,

[Borodog]

Looks like a Poisson distribtuion to me.

P(k,m) = [exp(-m) m^k]/k!

is the probability that there are exactly k occurances when m is the expected number of occurances (the average in your problem).

I think. I'm not a statistician.

[leafsrock]

I thought that might be the case but it just seemed too easy. So since for the 1st part k = 3 and m = 3, P(3,3) = [exp(-3)3^3) / 3! and for the 2nd, P(m,m) = exp(-m)m^m / m! ?
I'm not very good at stats but I have to take this course b/c it's a prerequisite for some other course... help

[Borodog]

Looks right to me.

[leafsrock]

thanks for the help borodog.