Set X has x members, Set Y has y members. Set Z is....

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Love21

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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 ?

(a) x + y + k
(b) x + y - k
(c) x + y + 2k
(d) x + y - 2k
(e) 2x + 2y -2k

So i plugged in numbers to start. x = 10, y = 12 and z = ?
How do you proceed on this problem? I really am not sure where to begin, any help or suggestions are welcome.
 
Re: Set x...

The set in question is known as the symmetric difference of X with Y.
The number of elements in the symmetric difference equals the sum of the number in each set minus twice the number common to both.
Now which option fits that description and WHY?
 
Re: Set x...

Item (c) has a plus not a minus.
 
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