n(A gabungan B) = 43, dan n(A irisan B) =5. jika n(A) adalah 3 kalinya n(B), maka n(B) ....

n(A U B) = 43
n(A iris B) = 5
n(A) = 3n(B)
n(B) = ?

n(A U B) = n(A) + n(B) - n(A iris B)
43 = 3n(B) + n(B) -5
43 = 4n(B) - 5
4n(B) - 5 = 43
4n(B) = 43 + 5
4n(B) = 48
n(B) = 48/4
n(B) = 12