Let's say we want to reduce:
10
----
15
Here's an example:
Fraction: 10/15.
Factors:
10: {1, 2, 5, 10}.
15: {1, 3, 5, 15}.
GCF: 5.
Divide the numerator and the denominator:
10/5 = 2.
15/5 = 3.
Answer: 2/3.