00:01
In this situation, they tell us that a student takes a multiple choice test with 10 questions, and each question has two choices, and the student is going to guess randomly at each question.
00:11
So first we want to compute the probability that he's going to be get it right.
00:17
So the probability is going to be, if he's guessing, that probably is going to be one out of two, which is 0 .5.
00:24
Now, this is what we consider a binomial situation.
00:26
There's a fixed number of trials, 10 to 10 questions.
00:31
And there's a fixed probability of each one the probability that he can guess each one is 0 .5 so this one is what we call a binomial situation or binomial distribution situation so here when we want to compute probabilities we're going to compute probabilities with the binomial distribution so right here they want the probability that we get two right two equations right so this can be easily done with a calculator graphical calculator that is all graphical calculators have the binomial distribution so in this case is clean the screen we go to distributions like in this is a t i84 which is a very popular high school calculator so distributions here in blue second distributions we look for the binomial and we find two the binomial pdf and the cdf the pdf the pdf is for the specific value like in this case for x equals to 2 so we do that and the number of trials is 10 the number of the probability success of getting the question right is 0 .5 and we want to know what the probability of getting exactly 2 is so we compute that and we get a value of 0 .0 .039 with 4 decimal places like they want 0 .0 .039 now in the next question they want the probability that the number of correct ones is greater than 3.
02:04
And some calculators you can actually do this, but in the ti -84, you have to go a little bit around that and do it as one minus the probability that x is less or equal than 3...