n(A) = 20
n(B) = 30
n(A∪\cup∪B) = 40
n(A∩\cap∩B) = …
10
20
30
40
Menggunakan rumus
n(AB)= n(A)+n(B)-n(AB)
maka
40 = 20 + 30 - n(A∩\cap∩B)
n(A∩\cap∩B) = 20 + 30 - 40
n(A∩\cap∩B) = 50 - 40
n(A∩\cap∩B) = 10