Correct Answer - Option 3 : 21
Given:
Total students = 80
Number of students who bought cake = 57
Number of students who bought cookies = 44
Calculation:
Number of students, n(A∪B) = 80
Number of students bought cake, n(A) = 57
Number of students bought cookies, n(B) = 44
Let, number of students bought both cake and cookies, n(A∩B) = x
According to set theory formula,
⇒ n(A∪B) = n(A) + n(B) – n(A∩B)
⇒ 80 = 57 + 44 – x
⇒ x = 101 – 80
⇒ x = 21
∴ Number of students who bought both cake and cookies = 21