calculus and probability help

the question is:

the chance that a certain species of plant survives frost is 4 in 5. If three of these plants are selected at random, what is the probability that

i) none of the plants survive

ii)exactly two pplants survive

im not sure how im supposed to work it out and give my answer.

Also, another question is:

on a three wheel poker machine, there are 20 symbols one each wheel. There are five aces on the first wheel, one ace of the second wheel, and three aces on the third wheel. what is the probability that:

i) 3 aces will show across the centre line

ii) at least one ace will show on the centre line

Please help and explain. Thank you

Re: calculus and probability help

Just to get you started. P (1 plant not surviving)= 1/5) So 3 not surviving P=(1/5)^3

Exactly 2 out of 3 surviving means SSN or SNS or NSS Each one of these Ps = (4/5)^2*(1/5) So when you add them you get 3*(4/5)^2*(1/5)