In this worksheet, we will practice identifying prime and composite numbers and differentiating between them.

**Q2: **

Is 21 a prime or a composite number?

- A a composite number
- B a prime number

**Q3: **

Is 23 a prime or a composite number?

- A a prime number
- B a composite number

**Q4: **

All prime numbers are odd except .

**Q5: **

Determine whether the number 85 is prime, composite, or neither.

- Aneither prime nor composite
- Bprime
- Ccomposite

**Q6: **

Fady is learning about prime numbers. He knows that 5 is a prime number, because the only factors of 5 are 1 and 5.

Is 9 a prime number? Why?

- A No, because 3 is a factor.
- B Yes, because its only factors are 1 and 9.

**Q7: **

Maged says that 1 is a prime number because it only has 1 factor pair.

Is he correct? Why?

- A No, because all odd numbers are prime.
- B Yes, 1 only has one factor.
- C Yes, because all odd numbers are prime.
- D No, prime numbers have two factors, 1 only has one factor.
- ENo, prime numbers have more than two factors, 1 only has one factor.

**Q8: **

Mariam says that every even number is composite because 2 is a factor.

Is she correct? Why?

- A Yes, because all odd numbers are prime.
- B Yes, because 2 is an even number.
- C Yes, because 2 is even and composite.
- D No, because 2 is even and prime.
- E No, because 2 is even and composite.

**Q12: **

A teacher asked her class to colour all the prime numbers between 1 and 10. Here are some of their answers. Which one is correct?

- A
- B
- C
- D
- E

**Q13: **

Nada bought these four raffle tickets, and one of them was the winning ticket.

- A ticket number 34
- B ticket number 15
- C ticket number 23
- D ticket number 17
- Eticket number 18

**Q14: **

Which of the following is a prime number?

- A 4
- B 8
- C 45
- D 43

**Q15: **

Is 96 a prime number?

- Ano
- Byes

**Q16: **

Are the numbers 2, 47, and 79 prime numbers?

- Ayes
- Bno

**Q17: **

Which of the following is not a prime number?

- A2
- B23
- C73
- D68

**Q18: **

Find a prime number between 37 and 46.

**Q19: **

Look at these numbers.

How many of these numbers are prime?

Which is the largest prime number?

Which is the smallest composite number?

**Q20: **

State two prime numbers that are greater than 15 and less than 95.

- A45, 61
- B44, 60
- C42, 58
- D43, 59

**Q21: **

All odd numbers greater than 7 can be expressed as the sum of three prime numbers. Which three prime numbers have a sum of 97?

- A17, 18, 62
- B16, 20, 61
- C18, 19, 60
- D17, 19, 61

**Q22: **

Find the smallest prime number that is greater than 40.

**Q23: **

Which of the following integer sequences is not guaranteed to have infinitely many primes?

- A
- B
- C
- D

**Q24: **

How many prime numbers have integers as their square roots?

**Q25: **

How many prime numbers are there, and why?

- AWe do not know, because computers are not powerful enough to compute as largely as we need.
- BFinitely many, because once you reach a certain size, every number factors into smaller primes.
- CInfinitely many in theory, as you could theoretically extend the sieve of Eratosthenes indefinitely.
- DInfinitely many, otherwise you could simply take the product of all of them and add one.