00:01
This problem has a couple of probabilities dealing with two dice.
00:03
So the first is what's the probability of getting a sum of one or a sum of 12? so that's just two of the dice in the 36 system.
00:12
So it's going to be two out of 36, which is one out of 18 chance.
00:22
B is a sum of 7 or a sum of 11.
00:28
So we're going to add the two probabilities.
00:30
So to get a sum of 7, that would be.
00:37
Well, let's write right out the possibilities.
00:39
So we have 1 and 6, 2 and 5, 3, and 4, 4 and 3, 5 and 2, 6 and 1.
00:51
So the probability of getting a 7 is 6 out of 36.
00:57
And the probability of getting 11 is 2 out of 36, either a 5, 6 or a 6, 5.
01:03
So that's just going to be 8 out of 36, which is 4 out of 18, which is 2 out of 9.
01:15
Part c, an even numbered sum or a prime sum.
01:23
So the sums can only be 2 through 12.
01:28
This is an or, right? or.
01:31
Okay, so if we think back to our chart, the even numbers that we can get are 2, 4, 6, 8, 10, and 12.
01:47
Okay, there's only one way to get 2, 1 way to get 12.
01:52
There's three for 10.
01:54
That's 4, 6, 5, 5, 6, 4.
01:57
There's 3 for 4, 1, 3, 2, 2, 3 .1.
02:01
For 6, there's going to be 5, and for 8, there's going to be 5.
02:07
Five ways to get it, that is.
02:09
Okay.
02:11
So, grand total for getting an even sum, we're going to have 4 plus 5 is 9, plus 5 is 14, plus another 4 is 18.
02:21
So 18 out of 36, which is which is one half.
02:27
Okay, and then the second part was even though some or a prime sum.
02:37
So a prime sum would be anything that adds to two, three, five, seven, and eleven.
02:50
Okay, so to get a two, there's only one way to do that.
02:52
To get a three, there's two ways.
02:54
To get a five, there's four ways.
02:58
To get a seven, there's six ways.
03:00
And to get an 11, there's two ways.
03:04
Okay.
03:05
So that's going to be 3, 7, 13, 15.
03:09
So 15 out of 36...