Boolean Expression Problem

Question

$$AB'C'D+ABCD$$ $$=AD(B'C'+BC)$$ $$=AD$$

I have simplified this expression right but for some reason I still get the answer wrong. The expression $AD$ does not match the original truth table. Please help.

Answer 1

Note that $B'C' \ne (BC)'$

$$AB'C'D + ABCD = AD(B'C' + BC) = AD((B+C)'+BC)$$