Following a thread recently posted, binomal distribution answers the 'how many I need to get right' question. Say that I am a slacker and only want a 70% on a 40 question 4 answer, multiple choice test. For some odd reason, people would think that I would require to learn 18 questions.
40 * 70% = 28
40 * 25% = 10
28 - 10 = 18
However, if we follow binomal distribution...
f(x,n,p) = [n x]*p^x*(1-p)^(n-x) where x is number of trials, n is number of successes and p is chance of success.
So, if I want at 70 or higher on my exam with a 82% chance of succeeding, I want to know 20 questions. Same principle says to make a 90, I need to know 28 questions, not 26.