Yup, glad to hear that you also think the OA to the first one should be '10%' Stuart.
Mutual_help,
the formula you used is wrong,
when you say,
n(A int B) + n(A int C) + n(B int C), elements of (A int B int C) are included 3 times in this....
hence, you have to subtract - 2 X n(A int B int C) from the answer you are getting to get the right answer.
hence, it will be, 20 - 2(5) = 10%.
Set Theory.. What is the difference between these two
Stuart can you please explain the two problems with help of the equation mentioned by Ronnie. I mean this equationStuart Kovinsky wrote: Note that this method is really just another way to apply the 3 set equation quoted by Ronnie. If you're an equation person, it's a good equation to know. However, like most questions on the GMAT, you can often reason your way to the correct answer even if you don't know the right formula.
Total = Group1 + Group2 + Group3 - (sum of 2-group overlaps) - 2*(all three) + Neither
