GB-09-02-001 · Highest common factor

Find the highest common factor of 15 and 43.

Highest Common Factor (HCF via Venn Diagram) Booklet p. 42

Method

1) Find prime factors of both numbers

2) Place shared primes in the intersection of a Venn diagram

3) HCF = product of intersection (or 1 if coprime)

Worked Example (GB-09-02-001)

Prime factorise each number:

15=3\times5

43=43

Place each shared prime in the intersection once. Multiply the intersection: HCF = 1.

Ans = 1