Let A and B are sets with A11 B12 and AUB15 a find the numbe

Let A and B are sets with |A|=11, |B|=12, and |AUB|=15,

a) find the number of 2-element subsets A and B have in common

b) find |P(A-B)|

Solution

a)

|A and B| = |A| + |B| - |AUB|

Number of 2-element subsets A and B have in common = 11+12 -15 = 8 Answer

b)

|P(A-B)| = (11-8)/15 = 1/5 = 0.2 Answer