# Homework Help: Binomial distribution

1. Jul 27, 2013

### aaaa202

1. The problem statement, all variables and given/known data
In a class with 20 and one with 10 students each student has a probability of 0.3 to not show up on a particular day. On a given day, which class is most likely to have the highest ratio of absent students? This was in my exam, unfortunately I did not know how to do it.

2. Relevant equations
The probability that n students are absent on a given day in one class is binomially distributed.
I heard some say that since the relative standard deviation goes like 1/√N the class with fewer pupils is most likely to have most absent, but I am not sure about this.

3. The attempt at a solution
You could do a whole lot of counting, but I don't think that's the point. Besides it would be a very tedious proces. I did it with a class of 1 and 2 students and counting even then took time.

2. Jul 27, 2013

### tiny-tim

hi aaaa202!

(i haven't actually tried this , but …)

i think i'd calculate Pk, the probability that exactly k students out of 30 are absent

and then for each k the probability Qk that less than one third of k from 30 come from the 10