GCF (HCF) of 18 and 15

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Greatest Common Factor of
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What is the Greatest Common Divisor of 18 and 15?

Answer

GCF (HCF) of 18 and 15 is
3

Common factors: 1, 3

3 divides both: 18 ÷ 3 = 6, 15 ÷ 3 = 5 — and 6 and 5 share no factor but 1, so no larger number divides both.

18 = 2 × 32

15 = 3 × 5

Prime1815Lowest power
22——
33233
5—5—

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

GCF = 3

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GCF Table

Number 1Number 2GCF
18126
18142
18153
18202
18213
18222
18231
18246
18251
18262
18279
18282
18306
18311
18322
18333
18342
18351
183618
18371
18382
18393
18402
18426
18431
18459
18462
18471
18486
18491

FAQ

What is the Greatest Common Divisor of 18 and 15?

GCF (HCF) of 18 and 15 is 3

How to find the GCF of 18 and 15?

You can find the GCF of 18 and 15 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 18 and 15 is 3.

What prime factors do 18 and 15 share?

The prime factorizations of 18 and 15 have 3 in common, and multiplying those shared primes gives 3 — exactly the greatest common factor.

How does the GCF reduce the fraction 18/15?

Divide the numerator and the denominator by the GCF 3: 18 ÷ 3 = 6 and 15 ÷ 3 = 5. So 18/15 in lowest terms is 6/5.

See Also