1.

In a class of 50, 20 students like mathematics, 15 like science and 5 like both mathematics and science. Find the number of students who do not like any of the 2 subjects.1. 252. 103. 154. 20

Answer» Correct Answer - Option 4 : 20

Concept: 

Set theory:

  • A ∪ B means set of all the values in the set A and B.
  • ∩ B is the set of common elements in 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)
  • A' = U - A, where U is a universal set given and A is any set
  • A - B = set values of set A not in set B

 

Calculation:

Set A of students who like mathematics, so n(A) = 20

Set B of students who like science, so n(B) = 15

Given n(A ∩ B) = 5

Set of students who like at least one of the 2 given subjects is A∪B 

n(A ∪ B) = n(A) + n(B) - n(A ∩ B)

n(A ∪ B) = 20 + 15 - 5 = 30

Students who do not like either of the subjects = Total students - n(A ∪ B)

N = 50 - 30 = 20



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