Calculate all the prime factors for the numerator and write them down. Prime factors are a set of prime numbers that, when multiplied together, equal the number you're factoring. If 20/32 is the fraction you want to reduce, the calculation for the numerator will be 2*2*5=20, so the prime factors are 2, 2, 5.
Calculate all the prime factors for the denominator and write them down. If 20/32 is the fraction you want to reduce, the calculation for the denominator will be 2*2*2*2*2=32, so the prime factors are 2, 2, 2, 2, 2.
Combine equal terms into fractions. In this example, the numerator and the denominator have two 2's in common, 2/2 and 2/2 are the common terms. Scratch out or erase the common terms from the list you wrote earlier so you do not accidentally use them again later.
Write the remaining numerator and denominator factors in fraction form. For the numerator, it is 5/1 and for the denominator, it is 1/2, 1/2, 1/2.
Multiply all the resulting fractions together. Remember that any fraction that has the same numerator and denominator equals one.
2/2*2/2*5/1*1/2*1/2*1/2 = 1*1*5/(2*2*2) = 5/8.
5/8 is the reduced form of 20/32.