If M∩N=∅, n(M∪N)=18 and n(N)=13, then n(M) is _____ .
0
18
13
5
Given that,
M∩N=∅ ⇒n(M∩N)=0
⇒ Sets M and N are disjoint, i.e. there are no common elements.
n(M∪N)=18 and n(N)=13 ⇒n(M)=n(M∪N)−n(N)
⇒n(M)=18−13=5