Question

If A = {x: x = 2n+1, n ∈ N and 3 ≤ n ≤ 9},then the cardinality of A is .

• A. 3
• B. 9
• C. 7
• D. 6

Answer 1

The correct option is C 7

The elements of A satisfy the condition that they are of the form $2n+1,$ where $n$ is a natural number between 3 and 9.
Hence, the cardinality of A is the number of natural numbers between 3 and 9, including 3 and 9.
This number is 7 as A = {7,9,11,13,15,17,19}.