Question

Complement of the expression  A’B + CD’ is _________

(a) (A’ + B)(C’ + D)

(b) (A + B’)(C’ + D)

(c) (A’ + B)(C’ + D)

(d) (A + B’)(C + D’)

I got this question in a national level competition.

My doubt stems from Boolean Logic Operations topic in section Boolean Algebra and Minimization Techniques and Logic Gates of Digital Circuits

Answer 1

Correct answer is (b) (A + B’)(C’ + D)

Easy explanation: (A’B + CD’)’ = (A’B)'(CD’)’ (By DeMorgan’s Theorem) = (A” + B’)(C’ + D”) (By DeMorgan’s Theorem) = (A + B’)(C’ + D).