GCF for 15, 20 and 42

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Greatest Common Factor of
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What's the Greatest Common Factor (GCF) of 15, 20 and 42?

Answer

GCF of 15, 20 and 42 is
1

Common factors: 1

Only 1 divides all three: no prime is a factor of each of 15, 20 and 42.

Pairs do share factors — GCF(15, 20) = 5, GCF(15, 42) = 3, GCF(20, 42) = 2 — just none greater than 1 common to all three.

15 = 3 × 5

20 = 22 × 5

42 = 2 × 3 × 7

Prime152042Lowest power
2—222—
33—3—
555——
7——7—

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

GCF = 1

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GCF Table

1st2nd3rdGCF
1520271
1520281
1520291
1520305
1520311
1520321
1520331
1520341
1520355
1520361
1520371
1520381
1520391
1520405
1520411
1520421
1520431
1520441
1520455
1520461
1520471
1520481
1520491
1520505
1520511
1520521
1520531
1520541
1520555
1520561

FAQ

What's the Greatest Common Factor (GCF) of 15, 20 and 42?

GCF of 15, 20 and 42 is 1

What prime factors do 15, 20 and 42 share?

None at all: 15, 20 and 42 have no prime factor in common, so the only positive integer dividing all three is 1 and their GCF is 1.

Can you get the GCF of 15, 20 and 42 two numbers at a time?

Yes. The GCF of 15 and 20 is 5, and the GCF of 5 and 42 is 1 — 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 15 : 20 : 42?

Divide every term by the GCF 1: 15 ÷ 1 = 15, 20 ÷ 1 = 20 and 42 ÷ 1 = 42. So 15 : 20 : 42 in lowest terms is 15 : 20 : 42, and no whole number other than 1 divides all three of those.

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