Suat AyözProblem for April 11th from the 2026 AMS Daily Epsilon of Math Calendar
Alex Bolton@PercyButtons3 @DailyEpsilon Since only 3 elements are in S but not in A or B, the union of A and B has 27 - 3 = 24 elements. If we calculate |A| + |B| we count every element of the intersection twice and each element that is in A or B but not in the intersection only once. So |A| + |B| - |A u B| = |A n B|. So the intersection has 17 + 18 - 24 = 11 elements
rtn@alexdbolton @PercyButtons3 @DailyEpsilon Nice! I thought about it differently. A has 17 elements, so it's 27 - 17 = 10 elements that's not in A and 10 - 3 = 7 elements that's in B but not in A which gives 18 - 7 = 11 elements in B and in A