00:01
Okay, in this problem, we have a multiple choice test that contains 20 questions, and each of those questions has five choices for the correct answer.
00:07
So if we go about guessing, then what is the probability of getting 70 % of them correct? so first of all, we need to do what is 0 .7 of 20? come on, peter.
00:18
What is 0 .7 of 20? 70 % of 20.
00:21
Well, that's going to be 14.
00:22
So we're saying what's the probability of getting 14 correct? so the way we're going to do this is we're going to set n equal to 20 because we have 20 questions.
00:29
We're saying what's the probability that we get exactly 14 of them correct now the probability of getting one of them correct well there are five questions and only one of them is correct so that's one out of five that's going to be point two so point two right and then we're going to say that we're saying what's the probability of getting exactly that many so we're going to say the probability of getting big x equal to little x so this is a binomial probability problem meaning binomial there's only two outcomes for each one we either get it wrong or we get it right.
01:02
We have a fixed number of trials, meaning there's only 20 questions on the test.
01:06
Each one of them is independent, meaning my guess on one question doesn't affect my guess on another question.
01:14
And we're saying the probability of getting one right is the same each time.
01:18
And we're saying what is the probability that i get exactly 14? so that's a binomial probability problem.
01:24
So i'm going to go onto an online search engine and i'm going to type in binomial probability calculator.
01:30
And i'm going to put all of these parameters in...