Question

Set X has x members and set Y has y members. Set Z consists of all members that are in either set X or set Y with the exception of the k common members (k>0). Which of the following represents the number of members in set Z? x+y-k or x+y-2k or x+y+k or 2x+2y-2k

Answer 1

If you have a bag X of x pieces of fruit and a bag Y of y pieces of fruit and k fruit are found in both bags, then combining the bags and taking away the fruit means that you take all of the fruit from X and put them with all of the fruit from Y. Then you have to take away the k common fruit from each bag. If you take k fruit from two bags, then you have three k.

The answer is x+y-k-k

I know. I'm pretty good at math ... and analorgies.