GCF (HCF) of 15 and 9

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What is the Greatest Common Divisor of 15 and 9?

Answer

GCF (HCF) of 15 and 9 is
3

Common factors: 1, 3

3 divides both: 15 ÷ 3 = 5, 9 ÷ 3 = 3 — and 5 and 3 share no factor but 1, so no larger number divides both.

15 = 3 × 5

9 = 32

Prime159Lowest power
33323
55——

— = 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
1555
1563
1593
15105
15123
15161
15171
15183
15205
15213
15221
15231
15243
15255
15261
15273
15281
15291
153015
15321
15333
15355
15363
15381
15405
15423
15441
154515
15483
15491

FAQ

What is the Greatest Common Divisor of 15 and 9?

GCF (HCF) of 15 and 9 is 3

How to find the GCF of 15 and 9?

You can find the GCF of 15 and 9 by listing all factors of both numbers and picking the greatest common one, or by prime factorization. The GCF of 15 and 9 is 3.

What prime factors do 15 and 9 share?

The prime factorizations of 15 and 9 have 3 in common, and multiplying those shared primes gives 3 — exactly the greatest common factor.

How does the GCF reduce the fraction 15/9?

Divide the numerator and the denominator by the GCF 3: 15 ÷ 3 = 5 and 9 ÷ 3 = 3. So 15/9 in lowest terms is 5/3.

See Also