Question

If B⊆ A then n(A∩B) is
(a) n(A–B)
(b) n(B)
(c) n(B – A)
(d) n(A)

Answer 1

A set A is a subset of set B, denoted, A ⊆ B, if every element x of A is also an element of B.That is, A ⊆ B if ∀x(x ∈ A → x ∈ B).
For example :- Let R = {1, 2, 3, 4} and S = {1,2,3,4,5,6,7}
Then, R ⊆ S e.g., R is subset of S.

Here, B ⊆ A . Means B is subset of A
For understanding let an example B = {1,2} and A = {1,2,3,4,5}
n(A ∩ B) = number of common elements of both sets = 2
e.g., B = {1, 2} = A ∩ B
so, we can say that n(B) = n(A ∩ B)
Hence, option (b) is correct

Answer 2

Option ( b ) correct.

Reason .

If B subset or equal to A

then A Intersection B = B

n( A Intersection B ) = n( B )

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