Poisson probability distribution Question....Stuck!

Hey would really, really appreciate some help with this question on poisson distribution, this is like the only thing on my stats module so far I cant seem to understand. Lol, it just won't seem to click.

Q:

Estimate the number of serious road accidents a company can expect during mining operations. They know the average number of accidents on this type of mining site is .5 and follows a poisson distribution.

Calculate the probability that

(i) less than 2 accidents on site A

(ii) more than 4 accidents on site A

(iii) 3 or more accidents in total on all 3 sites

So, is it something like this?

Less than 2 accidents, P(X<2) = P(0)+P(1)

I am confused http://forumserver.twoplustwo.com/im...lies/frown.gif

Thank you!