Maths Probability problem

nailforhammer

OK so our teacher gave us a question to do a few weeks ago and I never got the answer off him and it's annoying me now. I was wondering if anyone could help? It actually pretty relevant haha.

The question is:
"Art is studying for his Leaving Certificate but has left his English study pile up. He wanst to know how risky it would be if he only studied 4 poets for the exam. If 4 poets come out of a total of 8 calculate the probability that none of the poets he studies come up."

Anyone know the correct answer?

robman60

It's 4/8 x 3/7 x 2/6 x 1/5 = 1/70

Think of reading your English paper from the top down. You read the first on the list and it's Mahon. Oops, I haven't studied him. That leaves 3 poets I haven't done and 4 I have done. Next one on the page is Plath. Oops, I haven't studied her. That leaves 2 poets I haven't studied and 4 I have etc.

nailforhammer

robman60 wrote: »

It's 4/8 x 3/7 x 2/6 x 1/5 = 1/70

Think of reading your English paper from the top down. You read the first on the list and it's Mahon. Oops, I haven't studied him. That leaves 3 poets I haven't done and 4 I have done. Next one on the page is Plath. Oops, I haven't studied her. That leaves 2 poets I haven't studied and 4 I have etc.

Thanks so much. So then if it was 'What is the probability that at least 1 comes up' that would be a Bernoulli's trial, would it?
Or would it just be 1 - 1/70 = 69/70?

robman60

nailforhammer wrote: »

Thanks so much. So then if it was 'What is the probability that at least 1 comes up' that would be a Bernoulli's trial, would it?
Or would it just be 1 - 1/70 = 69/70?

Just 1- 1/70 = 69/70

Bernoulli trials applies when each event is independent, which isn't the case here.