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7. Greatest Common Divisor (GCD)

The greatest common divisor, or GCD, of numbers $$a$$ and $$b$$ is the largest whole number $$m$$ such that $$m$$ divides $$a$$ and $$m$$ divides $$b.$$

The greatest common divisor is sometimes called the highest common factor, or hcf.

Example: Find the GCD of $$4$$ and $$6.$$

Solution $$\downarrow$$

The divisors of $$4$$ are $$1,2,$$ and $$4.$$ The divisors of $$6$$ are $$1,2,3,$$ and $$6.$$ The common divisors are $$1$$ and $$2.$$ So, $$2$$ is the GCD.

Find the GCD of these two numbers.