1.

Find the cardinal number of the following sets. (i) A = {x : x is a prime factor of 12}. (ii) B = {x : x ∈ W, x ≤ 5}.(iii) X = {x : x is an even prime number}

Answer»

(i) Factors of 12 are 1, 2, 3, 4, 6, 12. So, the prime factors of 12 are 2, 3.

We write the set A in roster form as A = {2, 3} and hence n(A) = 2. 

(ii) In Tabular form B = {0, 1, 2, 3, 4, 5} 

The set B has six elements and hence n(B) = 6 

(iii) X = {2} [2 is the only even prime number] 

∴ n (X) = 1



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