Question

numbers less than 20 which have exacly 3 factors pls!

Answer 1

Answer:

4 & 9 is a number less than 20 which have exactly 3 factors.

Step-by-step explanation:

Factors of 4 are 1, 2 and 4. Factors of 9 are 1, 3 and 9.

Answer 2

Answer:

  4 and 9

Step-by-step explanation:

A number will have exactly three (3) divisors if it is the square of a prime number.

Domain of interest

We can find the numbers of interest by looking for primes whose squares are less than 20. That is, we're interested in primes less than √20 ≈ 4.4.

There are two (2) such primes: 2 and 3.

Numbers of interest

The numbers we want are ...

  2² = 4, has divisors 1, 2, 4

  3² = 9, has divisors 1, 3, 9

The numbers 4 and 9 have exactly 3 divisors.