GCF for 18, 30 and 42

"Greatest Common Factor of 3 Numbers" Calculator
Greatest Common Factor of
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What's the Greatest Common Factor (GCF) of 18, 30 and 42?

Answer

GCF of 18, 30 and 42 is
6

Common factors: 1, 2, 3, 6

6 divides all three: 18 ÷ 6 = 3, 30 ÷ 6 = 5, 42 ÷ 6 = 7 — and 3, 5 and 7 have no factor but 1 common to all of them, so no larger number divides all three.

18 = 2 × 32

30 = 2 × 3 × 5

42 = 2 × 3 × 7

Prime183042Lowest power
22222
332333
5—5——
7——7—

— = power 0: the prime is not a factor of this number, so it cannot be in the GCF.

GCF = 2 × 3 = 6

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GCF Table

1st2nd3rdGCF
1827303
1828302
1829301
1830306
1830311
1830322
1830333
1830342
1830351
1830366
1830371
1830382
1830393
1830402
1830411
1830426
1830431
1830442
1830453
1830462
1830471
1830486
1830491
1830502
1830513
1830522
1830531
1830546
1830551
1830562

FAQ

What's the Greatest Common Factor (GCF) of 18, 30 and 42?

GCF of 18, 30 and 42 is 6

What prime factors do 18, 30 and 42 share?

All three factorizations contain 2 × 3, and multiplying those shared primes gives 6 — exactly the greatest common factor.

Can you get the GCF of 18, 30 and 42 two numbers at a time?

Yes. The GCF of 18 and 30 is 6, and the GCF of 6 and 42 is 6 — the same answer, because the greatest common factor is associative and does not depend on the order of the three numbers.

How does the GCF simplify the ratio 18 : 30 : 42?

Divide every term by the GCF 6: 18 ÷ 6 = 3, 30 ÷ 6 = 5 and 42 ÷ 6 = 7. So 18 : 30 : 42 in lowest terms is 3 : 5 : 7, and no whole number other than 1 divides all three of those.

See Also