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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.