Question

Find the cardinal number for the set.A = {6, 12, 18,..., 42}The set is infinite.O n(A) = 4n(A) = 42O n(A) = 7

Answer 1

Notice that the arrangement of numbers present in the set is some multiples of 6, therefore the complete set is:

$A=\mleft\lbrace6,12,18,24,30,36,42\mright\rbrace\text{.}$

Therefore the number of elements of A is 7.

Answer: n(A)=7.