SOLUTIONS
NUMBER SENSE & NUMERATION: PRIME AND COMPOSITE NUMBERS
REMEMBER!
A factor is a whole number that divides another whole number without a remainder.
A prime number is a whole number whose only two factors are one and itself.
A composite number is a whole number that has more than two factors.
Examples:
The factors of 7 are 1 and 7.
The factors of 22 are 1, 2, 11 and 22.
7 is a prime number.
22 is a composite number.
Don’t forget to play Fruit Shoot – Primes & Composites first! Go to mathfrog.ca for the link.
1. List all of the factors of each of the following numbers.
a. 14 ___1, 2, 7, 14______________
f. 43 ___1, 43____________
b. 35 ___1, 5, 7, 35______________
g. 3 ___1, 3______________
c. 21 ___1, 3, 7, 21______________
h. 4 ___1, 2, 4____________
d. 17 ___1, 17__________________
i. 81 ___1, 3, 9, 27, 81______
e. 36 ___1, 2, 3, 4, 6, 9, 12, 18, 36__
j. 19 ___1, 19_____________
2. Write the prime numbers from Question 1. _____17, 43, 3, 19___________________
3. Write the composite numbers from Question 1._____14, 35, 21, 36, 4, 81__________
DID YOU KNOW?
In ancient Rome it was
considered a sign of leadership to
be born with a crooked nose.
FUN MATH FACT
The whole numbers 1 and 0
are neither prime nor
composite.
4. Put a checkmark in the appropriate box. Two have been done for you.
NUMBER
PRIME
67
12
56
29
23

COMPOSITE




NUMBER
49
11
9
20
51
PRIME
COMPOSITE
NUMBER

18
5
95
59
41




Expectation: Identify and explain the relationship between composite numbers and prime numbers
PRIME
COMPOSITE





5. For each composite number below, construct a factor tree to find the prime factors. Write
the prime factors in the blank provided. The first one has been done for you.
a.
c.
Prime factors: 2, 3 and 5
Prime factors: 2 and 3
b.
d.
Prime factors: 3 and 7
Prime factors: 2, 3 and 11
6. Circle each prime number below.
89
51
99
33
27
15
47
2
94
43
38
7
70
53
61
8
87
75
83
69
100
101
102
103
104
105
106
107
108
109
7. A two-digit number is prime. When you reverse the digits, the new number is also prime.
There are nine numbers like this. List as many possibilities as you can. (Note: When you
reverse the digits of 18, you get 81.) Possible answers are 11, 13, 17, 31, 37, 71, 73, 79 or 97.
TRY THIS!
Can two prime numbers other than 2 and 5 ever have a
difference of 3? Explain why or why not.
No. Any two numbers that have a difference of 3 will
have one even number among them. 2 is the only even
prime number, so no other pair exists.
Expectation: Identify and explain the relationship between composite numbers and prime numbers