Sometimes you need not look too far and think too hard.
A pair of such numbers will be 3 and 12.
Surprised?
Factors of 3: 1, 3
Factors of 12: 1, 2, 3, 4, 6, 12
Thus, the gcf is 3.
Multiples of 3: 3, 6, 9, 12, 15, 18
Multiples of 12: 12, 24
Thus, the lcm is 12.