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GCF (HCF) of 20 and 42

"Greatest Common Factor" Calculator

What is the Greatest Common Divisor of 20 and 42?

Answer

GCF (HCF) of 20 and 42 is

2

Common factors: 1, 2

2 divides both: 20 ÷ 2 = 10, 42 ÷ 2 = 21 — and 10 and 21 share no factor but 1, so no larger number divides both.

20 = 2² × 5

42 = 2 × 3 × 7

Prime	20	42	Lowest power
2	2²	2	2
3	—	3	—
5	5	—	—
7	—	7	—

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

GCF = 2

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See Also

Least Common Multiple - Find the Least Common Multiple (LCM) of two numbers
Greatest Common Factor of 3 Numbers - Find the Greatest Common Factor (GCF) of three numbers
Least Common Multiple of 3 Numbers - Find the Least Common Multiple (LCM) of three numbers

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What is the GCF (HCF) of 20 and 42. The GCF of 20 and 42 is 2 — the biggest number that can divide both integers. Step-by-step GCF (GCD) calculation by factoring.

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GCF Table

Number 1	Number 2	GCF
20	21	1
20	22	2
20	23	1
20	24	4
20	25	5
20	26	2
20	27	1
20	28	4
20	30	10
20	32	4
20	35	5
20	36	4
20	38	2
20	39	1
20	40	20
20	42	2
20	44	4
20	45	5
20	47	1
20	48	4
20	50	10
20	55	5
20	56	4
20	58	2
20	59	1
20	60	20
20	70	10
20	75	5
20	84	4
20	90	10

FAQ

What is the Greatest Common Divisor of 20 and 42?

GCF (HCF) of 20 and 42 is 2

How to find the GCF of 20 and 42?

You can find the GCF of 20 and 42 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 20 and 42 is 2.

What prime factors do 20 and 42 share?

The prime factorizations of 20 and 42 have 2 in common, and multiplying those shared primes gives 2 — exactly the greatest common factor.

How does the GCF reduce the fraction 20/42?

Divide the numerator and the denominator by the GCF 2: 20 ÷ 2 = 10 and 42 ÷ 2 = 21. So 20/42 in lowest terms is 10/21.