00:01
Okay, we have two urns here.
00:03
One contains balls with numbers 1, 2, 3, 3.
00:07
That's a, and b contains balls 3 through 10.
00:11
First thing we do, we pick one of the two urns.
00:15
There's a one -half chance.
00:16
We pick a and a one -half chance.
00:19
We pick b.
00:20
And part a says, i want to work out the chance that the ball chosen is numbered 1.
00:27
Well, that only occurs with earn a.
00:31
So to get a ball number one will be one chance out of three.
00:40
Three balls, only one is labelled one.
00:44
So my answer then will be one half times one third, which is one out of six.
00:53
So part a then, the answer is one sixth.
00:57
Two things must happen.
00:58
You must choose urn a and you must pick the one.
01:03
So here then question a.
01:07
Now part b, what chance is there? the ball is numbered three.
01:11
In green here, to get three from earn a is also a one -third chance.
01:21
There are three balls.
01:22
Only one is label three.
01:25
So this way then will be one -half times one -third as well, which is also, of course, one -sixth...