To solve this ratio, we must first find the GCF, or the Greatest Common Factor, that is, the largest number that fits into both numbers. We can set up a table to compare the factors of each individual number, then identify common factors between the two numbers.
15 | 1 3 5 15 5 | 1 5
We see that the common factors include 1 and 5, however, 5 is the greatest common factor. Now we can simplify the ratio by dividing both numbers by 5.