Find the least common multiple of 9 and 15 -apex

Method 1:

List out the multiples of 9 and 15. Circle the common multiples. The smallest of this list of common multiples will be the answer.

Multiples of 9: 
9, 18, 27, 36, 45, 54, 63, 72, 81, 90, ...

Multiples of 15:
15, 30, 45, 60, 75, 90, 105, 120, ...

Common multiples:
45, 90, 135, ...

The smallest common multiple is 45. So the Least Common Multiple (LCM) is 45



Method 2:

Find the GCF of 9 and 15. This is 3 since it is the largest factor to go into both 9 and 15.

Multiply 9 and 15 to get 9*15 = 135

Divide that result over the GCF to get 135/3 = 45 which supports the result of method 1



Method 3:

List out the prime factorization of each number. Highlight the most frequent unique prime factors and multiply them together

Prime factorization of 9: 3*3
Prime factorization of 15: 3*5

The unique factors are 3 and 5. We have two copies of 3. So we have 3*3*5 = 9*5 = 45 as the LCM



No matter which method you pick, the final answer is 45

The answer would be 13.5 minutes.