00:01
Okay, in this question we are given some information about our set, a and b.
00:06
I mean, we know the number of a is equal to 35, number of b is equal to 15, and the number of the whole set is equal to 100, and the number of a intersecting b is 13.
00:19
We are required to compute some other number, to get some other information about set, about sets a and b.
00:29
Okay, and as we are given the venn graph, venn diagram, it's very easy to see what we're actually required to compute the number of this part and this part.
00:53
And we can see the number of the first part, a prime intersecting b, which is this one, is that will be actually equal to the number of the union minus the number of a, right? because the number of union is this one, and if we just subtracting a means we're subtracting this guy, then we'll get the number of a prime intersecting b, right? so, as na is given, we want to compute the number of a union b.
01:53
The number, by observation, we know the union will be actually equal to a, number of a plus the number of b, and minus the number of a intersecting b.
02:09
Why do we need to subtract something? because if we just add a and b, we are actually double counting the intersection.
02:21
So, just plug all terms into our expression, we know this will be actually equal to 35 plus 15 minus 15, which will be 55...