00:01
For this problem, for part a, we want to find the probability that it takes us one try to get through.
00:07
So that's just going to be 1 minus the probability that the line is busy when we call.
00:11
So that's 1 minus 0 .4 for a result of 0 .6.
00:17
Or, pardon me, wrong way around.
00:19
1 minus 0 .6 for a result of 0 .4.
00:22
For the probability that we get through on the second try, well, we'd have to get the line being busy on our first try, and then not busy on the second.
00:33
So that's going to be 0 .6 times 0 .4, which will be equal to 0 .24.
00:43
And then for the probability that we get through on the third try, we'd have to not get through on the first or second tries, and then get through on the third.
00:55
So that's going to be 0 .6 squared times 0 .4, for a result of 0 .144.
01:04
For part b, we're looking for the probability that it takes, a total of four tries for both of us to get through...