1.

In a group, 12 people like only guitar and 15 people do not like piano, if 30 people are there in the group how many are there who neither likes piano nor guitar?1. 52. 43. 34. 2

Answer» Correct Answer - Option 3 : 3

Concept: 

Set theory:

  • A ∪ B means set of all the values in the set A and B.
  • ∩ B is the set of common elements of A and B.
  • Subset (⊂) is the set such that all the elements of the subset are in the set from which the subset is taken from.
  • Number of elements in set A = n(A)
  • n(A ∪ B) = n(A) + n(B) - n(A ∩ B) = n(A) + n(B - A) = n(B) + n(A - B)
  • A' = U - A, where U is a universal set given and A is any set
  • n(A') = n(U) - n(A)
  • A - B = set values of set A not in set B
  • n(A - B) = n(A) - n(A ∩ B)

 

Calculation:

Let Set A of people who like piano and Set B of people who like guitar and U is set of all people

Given n(A') = 15 and n(B - A) = 12

As n(A') = n(U) - n(A)

⇒ 15 = 30 - n(A)

⇒ n(A) = 15 

Now, Set of people who likes at least one A∪B

n(A ∪ B) = n(A) + n(B - A)

n(A ∪ B) = 15 + 12 = 27

∴ People who do not like either of the two N = n(U) - n(A ∪ B) 

N = 30 - 27 = 3



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