OG PS-D14

by **Guest** Fri Jan 02, 2009 6:15 pm

i am working on a problem in the official guide book and i am confused about this questions.
A Venn Diagram is needed for this problem and in the solutions, it does not include the number in the shared part of the diagram when adding up the total.

Can someone explain why?

by **RonPurewal** Fri Jan 09, 2009 6:00 am

that's part of the quantity designated "x" in the problem. if you added it to x, you would actually be double-counting the shared region.

note: these sorts of problems are the best endorsement for our tried-and-true Double Set Matrix (the device we use to attack overlapping sets problems). when you use the double set matrix, each possibility gets a separate square in the grid, and you don't have to worry anywhere near as much about things like double-counts.