Answer
50
Work Step by Step
S= set of all novels at home
A= set of all ovens I have read
B= set of all novels my sister has read
We are given
n(S)= 400
n(A)=150
n(B)=200
n($A\cap B)$=50
so
n(A$\cup$B)=n(A)+n(B)-n($A\cap B)$=150+200-50=350,
(the number of novels read by either me or my sister)
$n(A\cup B)^{\prime}=n(S)-n($ A$\cup$B)$= 400-350 = 50$
(is the number of books neither of us have read)
