Suppose Set A contains 325 elements and the total number elements in either Set A or Set B is 631. If the Sets A and B have 43 elements in common, how many elements are contained in set B?
We have
Number in (A or B) = Number in (A) + Number in (B) - Number in (A and B)
So
631 = 325 + Number in (B) - 43
631 = 282 + Number in (B)
631 - 282 = Number in (B) = 349