00:01
In this exercise, we are told that there is a lab network consisting of 20 computers that has been attacked by a virus, and the virus enters each computer with probability 0 .4, independently of the other computers.
00:18
And we are asked for the probability that it enters at least 10 computers.
00:25
So let's let x be the number of computers that it entered.
00:35
So since the probability success is constant for each computer, that is, they are independent of each other.
00:43
And there's only two possibilities for the outcome for each computer.
00:46
Either it was attacked by the virus or it was not.
00:52
X is a binomial random variable.
00:59
And the binomial has two parameters, the probability of success, and the number of trials, so that's 0 .4, and the number of trials, which is 20.
01:14
So here we want the probability that x is at least 10, which is equal to 1 minus.
01:25
The probability that x is at most 9.
01:32
And this can be solved using software.
01:35
So let's use excel...