Start by writing down the first items to choose from. Below each one draw a line to each item you are to choose from next. If there was more you would just repeat this process, continually expanding outward. See the attached picture for your answer.
Note that both 12 and 30 are multiples of 2. Divide the numerator and denominator by 2. 6/15. Note that 6 and 15 are multiples of 3. Divide the numerator and denominator by 3. 2/5. Note that 2 and 5 are both prime numbers. Your answer is 2/5.
