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Let \(S = \{1, 2, \ldots, 180\}\). Define \(A\) as the set of all multiples of 4 in \(S\), \(B\) as the set of all multiples of 6 in \(S\), and \(C\) as the set of all multiples of 9 in \(S\). The…

Question and options

Let S={1,2,…,180}S = \{1, 2, \ldots, 180\}. Define AA as the set of all multiples of 4 in SS, BB as the set of all multiples of 6 in SS, and CC as the set of all multiples of 9 in SS. The number of elements in SS that belong to exactly one of A,B,CA, B, C is
  1. 50
  2. 40
  3. 48
  4. 44

Answer and explanation

Correct answer: A - 50
|A|=45, |B|=30, |C|=20, |A^B| (mult of 12)=15, |A^C| (36)=5, |B^C| (18)=10, |A^B^C| (36)=5. Exactly one = sum singles - 2*sum pairs + 3*triple = 95 - 60 + 15 = 50.

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  • IPMAT Indore

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