Using the prime factors method, what is the least common multiple of 12 and 18?
A24
B72
C216
D36
Answer & Solution
Correct answer: D. 36
1. Write 12 as the product of primes: 2 times 2 times 3.
2. Write 18 as the product of primes: 2 times 3 times 3.
3. Match the primes vertically where possible, so one column holds two 2s and another holds two 3s.
4. Bring down every column and multiply: 2 times 2 times 3 times 3 equals 36.
5. Multiplying 12 and 18 directly gives 216, which is a common multiple but far larger than the least one.
_Source: OpenStax Elementary Algebra (CC BY 4.0), Ch 1 "Foundations", section 1.1 Introduction to Whole Numbers_
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