Set U={1,2,3,4,5,6,7,8,9}, A={x:x∈N,30≤x2≤70}, B={x:x is a prime number <10}. Which of the following does NOT belong to the set (A−B)′ ?
A
4
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B
5
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C
6
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D
9
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Solution
The correct option is B6 Given, U={1,2,3,4,5,6,7,8,9} A={x:x∈N,30≤x2≤70} So, A={6,7,8} and A′={1,2,3,4,5,9} B={x:x is a prime number <10} So, B={2,3,5,7} and B′={1,4,6,8,9} ⇒A∩B={7} (A−B)′=U−(A−B)
=U−[A−(A∩B)] ={1,2,3,4,5,6,7,8,9}−[{6,7,8}−{7}] ={1,2,3,4,5,6,7,8,9}−[{6,8}] ={1,2,3,4,5,7,9} So, 6 and 8 does not belong to (A−B)′.