Misal n(S) - n(A) =5 dan 2n(S) - n(A) = 13 Banyak anggota A adalah .... A.3 B.5 C.8 D.10

n(S) - n(A) = 5
n(A) = 5 - n(S)

2n(S) - A = 13
2S - ( S - 5 ) = 13
2S - S + 5 = 13
S + 5 = 13
n(S) = 13 - 5 = 8
n(S) = 8

nS - nA = 5
8 - A = 5
n(A) = 8 - 5 = 3

Banyak anggota A = 3 (a)