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To determine the least common multiple of two numbers, determine the prime factors of both number. Then, determine the prime factors they have in common. Multiply all their prime factors together (in other words, multiply both numbers together) and divide by the prime factors they have in common (in other words, their greatest common factor).
The prime factors of 21 are 3 and 7.
The prime factors of 28 are 2, 2, and 7.
The prime factors in common are a single 7.
Therefore, the lowest common multiple is 21 x 28 ÷ 7 = 84
Wiki User
∙ 12y ago
Wiki User
∙ 15y agoThe least common multiple of 28 and 21 is 84
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What is The least common multiple of 21 35 and 28?
The LCM of 2135 and 28 is 8540 The LCM of 21, 35 and 28 is 420.
What is the LCM 21 and 28?
84
