LCM for 5, 7 and 21
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What's the Least Common Multiple (LCM) of 5, 7 and 21?
Answer
LCM of 5, 7 and 21 is
105
First common multiples: 105, 210, 315, …
105 is divisible by all three: 105 ÷ 5 = 21, 105 ÷ 7 = 15, 105 ÷ 21 = 5 — and 21, 15 and 5 have no factor but 1 common to all of them, so no smaller number is. As a common denominator: multiply the top and bottom of x/5 by 21 and of y/7 by 15 and of z/21 by 5.
5 — prime
7 — prime
21 = 3 × 7
| Prime | 5 | 7 | 21 | Highest power |
|---|---|---|---|---|
| 3 | — | — | 3 | 3 |
| 5 | 5 | — | — | 5 |
| 7 | — | 7 | 7 | 7 |
— = power 0: the prime is not a factor of this number; the LCM takes it from the number that has it.
LCM = 3 × 5 × 7 = 105
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See Also
- Greatest Common Factor of 3 Numbers - Find the Greatest Common Factor (GCF) of three numbers
- Least Common Multiple - Find the Least Common Multiple (LCM) of two numbers
- Greatest Common Factor - Find the Greatest Common Factor (GCF) of two numbers
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