Answer:
14
Step-by-step explanation:
The number of elements in M is 31, so let's make set M the set of the first 31 natural numbers.
M = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31}
Set N has 18 elements. We need to choose 18 elements to place in set N.
The union of sets M and N has 35 elements. That means that since set M contributes 31 elements to the union, set N only contribute 4 new elements to the union. That means that 14 of the 18 elements in N are in common with set M.
Set N can be:
N = {18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35}
Answer: 14
