00:01
So for this problem, i'll first note that if more than 80 rolls, if more than 80 rolls are needed, then we'd have that the average of the rolls, which is calculated by taking the sum of the rolls, divided by 80, must be less than or equal to what we need the sum to be, 300 divided by 80, and 300 over 80 is 3 .75.
00:45
So we have that the probability that the number of rolls is greater than 80 is equal to the probability that our sample mean value is less than 3 .75.
01:02
So, in order for that to be the case, well, we'll need to do some quick calculations.
01:09
We know that the mean value here it's going to be equal to, oh, actually, no, we're given it explicitly.
01:16
We're given that the expected value or the mean value is equal to 7 over 2 for each individual outcome.
01:23
And we have that the standard deviation would be equal to 35 over 12.
01:31
Then means that the standard deviation of our sample means, it's going to be 35 over 12, let's not 21, 12, divided by the square root of the sample size.
01:44
Now, here it's a little bit uncertain because of the fact that we are just going to keep on rolling until we exceed 300...