If A = {x : x is a prime number less than 10}, find the cardinality of A.
Answer: B
We need to list the prime numbers less than 10.
Prime numbers are natural numbers greater than 1 that have no positive divisors other than 1 and themselves.
The prime numbers less than 10 are 2, 3, 5, and 7.
So, A = {2, 3, 5, 7}.
The cardinality of A, denoted n(A), is the number of elements in the set, which is 4.