00:01
This problem, we want to choose two chips from chips numbered 1 to 8, and we want to sum of 7.
00:06
So we take two chips randomly from 8 chips.
00:08
That will be 8c2 as the denominator.
00:11
And then we just need to count the number of ways that we can add up to 7.
00:14
So that would be 1 .6.
00:16
Let me write this down.
00:17
1, 6, 25, and 3, 4.
00:22
We don't want to include 4, 3, 5, 2, or 6, 1 because in the denominator we said order doesn't matter.
00:27
Those will be three out of eight choose two.
00:34
That would be 28.
00:37
In part b, we want 20 chips.
00:41
There are 20 chips.
00:42
We want to choose two of them, so 20, c2.
00:44
And we want to count the number of ways that we can differ by three.
00:48
So we've got one, four.
00:51
We could have two, five, three, six, and so on, all the way up to 17 and 20.
01:00
So when we count the number of cases here, there are 17 cases.
01:05
That'll be 17 over 190.
01:13
In part c, we want to take two chips out of 20 again...