at most, at least, exactly...geometric probability & binomial probability

For example, I have a problem in my book, the probability of school having a contract is 0.62, and you have a random sample of 20 schools.

Whats probability at least 4 schools w/ contract?
Whats probability between 4 and 12 schools w/ contract?
Whats probability at most 4 schools w/ contract?

You don't have to answer the question...just maybe clarify:
if the problem says "at least" then p(none)-p(1)? wait I think this is wrong...oh and calculator keystrokes would be great btw...like binomcdf(...)

Basically just walk me through, any help is greatly appreciated