GCF for 5, 12 and 20

"Greatest Common Factor of 3 Numbers" Calculator
Greatest Common Factor of
,
and

What's the Greatest Common Factor (GCF) of 5, 12 and 20?

Answer

GCF of 5, 12 and 20 is
1

(One)

1 is the largest positive integer that divides 5, 12 and 20 without a remainder — every other common divisor of the three divides it too.

Finding the GCF of 5, 12 and 20 by Prime Factorization

Split all three numbers into prime factors, then keep every prime that appears in all three of them, each taken as many times as it appears in the poorest factorization. Multiplying what is left gives the greatest common factor:

All Prime Factors of 5: 5 (exponent form: 5)

All Prime Factors of 12: 2 × 2 × 3 (exponent form: 22 × 3)

All Prime Factors of 20: 2 × 2 × 5 (exponent form: 22 × 5)

Prime factor51220Lowest power
2—2222—
3—3——
55—5—

Not one prime factor is shared by all three numbers, which makes 5, 12 and 20 relatively prime as a set. The only positive integer dividing all of them is 1.

Checking the GCF of 5, 12 and 20 Two Numbers at a Time

The greatest common factor is associative, so three numbers can be handled as two pairs — and this is what makes the Euclidean algorithm usable here: run it on the first pair, then run it again on that result and the third number.

GCF(a, b, c) = GCF(GCF(a, b), c)

GCF(5, 12) = 1

GCF(1, 20) = 1

GCF(5, 12, 20) = 1

The answer checks out by division — all three quotients come out whole:

5 ÷ 1 = 5

12 ÷ 1 = 12

20 ÷ 1 = 20

5, 12 and 20 have no common factor left — that is what makes 1 the greatest one.

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See Also

About "Greatest Common Factor of 3 Numbers" Calculator

This calculator finds the Greatest Common Factor (GCF) of three numbers at once, without doing it in two passes. For example, it can help you find out what's the Greatest Common Factor (GCF) of 5, 12 and 20? (The answer is: 1). Enter the first number (e.g. '5'), the second (e.g. '12') and the third (e.g. '20'), then hit the 'Calculate' button.
The Greatest Common Factor of three numbers — also called the greatest common divisor (GCD) or highest common factor (HCF) — is the largest positive integer that divides all three of them with zero remainder
"Greatest Common Factor of 3 Numbers" Calculator
Greatest Common Factor of
,
and

GCF Table

Number 1Number 2Number 3GCF
55121
56121
57121
58121
59121
510121
511121
512121
512131
512141
512151
512161
512171
512181
512191
512201
512211
512221
512231
512241
512251
512261
512271
512281
512291
512301
512311
512321
512331
512341

FAQ

What's the Greatest Common Factor (GCF) of 5, 12 and 20?

GCF of 5, 12 and 20 is 1

What prime factors do 5, 12 and 20 share?

None at all: 5, 12 and 20 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 5, 12 and 20 two numbers at a time?

Yes, and it is the check this page prints. The GCF of 5 and 12 is 1, and the GCF of 1 and 20 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 5 : 12 : 20?

Divide every term by the GCF 1: 5 ÷ 1 = 5, 12 ÷ 1 = 12 and 20 ÷ 1 = 20. So 5 : 12 : 20 in lowest terms is 5 : 12 : 20, and no whole number other than 1 divides all three of those.

See Also