Page 27 - NUMINO TG_6A

Activity 3 The LCM of Three Numbers

jOb ective Find the LCM of three numbers.

1. Textbook Instructions Activity 3 The LCM of Three Numbers

Have students find the least common multiple Learn how to find the least common multiple of three numbers.
among three numbers.
Find the least common multiple of 6, 8, and 12.
Find the LCM of 6, 8, and 12. Find the common multiples of 6, 8, and 12.
Write a list of multiples for 6, 8, and 12, or Multiples of 6: 6, 12, 18, 24, 30,
use prime factorization to find the prime Multiples of 8: 8, 16, 24, 32, 40,
factors 6, 8, and 12. Multiples of 12: 12, 24, 36, 48,
Step 1: Prime factors of 6 Common multiples of 6, 8, and 12: 24, 48,
Find the smallest common multiple.
23 The LCM: 24
Step 2: Prime factors of 8
1 . Find the least common multiple of the three numbers.
222
Step 3: Prime factors of 12 a. 2, 6, 14 b. 9, 12, 18

223 The LCM: 42 The LCM: 36
Step 4: The LCM will contain each unique
c. 3, 8, 10 d. 12, 18, 30
prime group once. The LCM: 120 The LCM: 180
222
e. 7, 14, 28 f. 6, 10, 30
223 The LCM: 28 The LCM: 30
23

2 2 2 3 24: LCM

1. Have students find the LCM for each group
of numbers.

8

2. Build Understanding

Some students may need additional help finding the least common multiple among three numbers before
beginning the exercises. Solve the following example slowly for students.
Example: Find the LCM of 22, 34, and 68.
Step 1: List the prime factors for each number

22 2 11, 34 2 17, 68 2 2 17
Step 2: Multiply all of the unique prime groups.

2 2 17 11 748

010 NUMINO Teacher s Guide