Multiple choise test probability!? Help!!

teacher give a 20 question multiple choice test. There are 4 possible answers and only one is correct. Find the probability that the student..

a) Gets exactly 19 right

b)Gets at least 1 right

I'm guessing this has to do with binomial probability.. since there is 4^20 answers.

not sure how you would set this up. Any help is appreciated!

Okay, so for A) it would be 20C19 x (.25)^19x(.75)^1 ????? I got 5.46%?????

And for B)

1- minus part A , which is 99%

Right????