00:01
We are looking at three randomly chosen students who are taking a driver's exam.
00:06
They have an equal chance of passing and of failing.
00:10
So we have three people and equals three.
00:13
And the probability of passing the exam is 0 .5, 50%.
00:18
And of failing, 50%.
00:20
For question five, we want the probability they all pass.
00:27
So the key to this question is that these are independent trials.
00:34
Each one's probability of passing does not influence the others.
00:38
So if you want to combine trials, you just need to multiply.
00:50
So for part 5, we have the probability of the first one passing, 0 .5, multiplied by the second, 0 .5, multiplied by the third, 0 .5.
01:01
0 .5 to the power of 3, which is an 8th.
01:06
So the answer is d.
01:07
1 over 2 becomes 1 over 4, becomes 1 over 8.
01:13
Part 6, we want the probability, at most, one of them passes.
01:20
So x, the number who passes, who pass is at most 1.
01:24
It could be 1, it could be 0.
01:27
So how do we find it? i'm going to make this a little bit more complicated by providing the binomial formula.
01:37
Because this is a binomial distribution.
01:40
Three independent trials, two outcomes, same probability for each.
01:45
The probability of x of them passers.
01:47
Is n choose x, p to the x, 1 minus p to the n minus x...