00:01
We know that 61 % of internet users are more careful when using public wi -fi.
00:06
And we're looking at four randomly selected internet users.
00:09
So our sample size n is 4, and the probability, p, that each one is more careful, is 0 .61.
00:18
And we want the probability, but at least one of them is careful.
00:22
So if x is the number who are more careful, we want x to be at least one.
00:28
So how's we find that? so you could use the binomial formula to calculate the probability that one of them is careful, two of them are careful, three of them, four of them, and add those up.
00:40
But there's a faster way, and it's called the complement rule.
00:50
So we know, but when you ask these four people, are you more careful using public wi -fi? there are five possible outcomes.
00:57
Either none of them are, or one or two, or three, or four.
01:01
One of those five things is definitely going to happen.
01:04
We have a probability distribution here.
01:06
So, we can start at 1, the probability of 1 of the 5 outcomes will happen, and subtract the only outcome that does not meet this criteria.
01:16
But none of them are more careful.
01:20
And if none of them are more careful, well, that's the same thing happening four times in a row.
01:25
The probability is 0 .39, the probability of a particular one is not careful, to power of 4, because it happens four times in a row.
01:36
So if we just compute this, 0 .39 to power of 4 is 0 .0 .0 .0 .0 .3 .1...