Question

Which of the following have exactly four factors?

• A. 15
• B. 27
• C. 8
• D. 16

Answer 1

Answer: (A), (B), (C)

The correct options are
A

15

B

27

C

8

If a number is the product of two distinct primes, then it will have exactly four factors.

For example, consider the number $6=2\times 3$, where 2 and 3 are distinct primes. 6 has four factors in all - 1, 2, 3 and 6.

Also, if a number is a cube of a prime number, the number has exactly four factors.

For example, consider the number $8=2\times 2\times 2$. 8 has four factors in all - 1, 2, 4 and 8.
Now, in the options given, 15 is the product of two prime numbers 3 and 5,

27 is the cube of 3 and

8 is the cube of 2.