LCM lesson

Lowest common multiple (hiding numbers)

By Maria Woodbury

LCM

Write both numbers as a product of prime numbers
Then
Write the first number,
and add what is missing from the second number

12 = 2 x 2 x 3
15 = 3 x 5
The lowest common multiple is 2 x 2 x 3 x 5

Your turn!

What is the lowest common multiple of 21 and 32?

Step 1: 21 = 32 =





Step 2:

Match

Match the first three multiples to the numbers given

• 5

• 2

• 10

• 8

• 7

5, 10, 15

2, 4, 6

10, 20, 30

8, 16, 24

7, 14, 21

• 5, 10, 15

• 2, 4, 6

• 10, 20, 30

• 8, 16, 24

• 7, 14, 21

Categorize

Options (14)

24

36

48

72

84

96

108

30

45

75

90

105

120

135

Add the multiples to the correct numbers

12

15

Multiple Choice

The HCF of 12 and 15 would be

• 4
• 6
• 12
• 3

Multiple Choice

The LCM of 12 and 15 would be

• 30
• 45
• 75
• 60

Poll

I am confident to

• Find HCF and LCM

• Finding HCF at this stage

• Finding LCM- I forgot what HCF was

• doing factor trees