Which of the following integers is/are the product of exactly two different prime numbers? 21, 22, 23, 24, 25
Credited Answer(s): 21, 22
The correct answers are 21 and 22. Let's factor each possible answer. Choice A: 21 = 3 × 7 Choice B: 22 = 2 × 11. Choice C: 23 = prime number. Choice D: 24 = 2 × 2 × 3 × 3. Choice E: 25 = 5 × 5. Only the first two choices (21 and 22) are the product of exactly two different prime numbers.
 23 is also the product of the two following different prime numbers: 23 and 1
