$(1-\frac12)\times(1-\frac23)=\frac12\times\frac13=\frac16$. 
I ate half of an apple pie on Saturday and two thirds of the remainder on Sunday. What fraction of the pie was left for Monday? 
Options:
(A) None 
(B) $\frac12$ 
(C) $\frac13$ 
(D) $\frac23$ 
(E) $\frac16$ 