Directions
Sometimes we don’t see the greatest common denominator (the largest number that can evenly divide both terms in the ratio) right away. In that case, we can begin by using any number that divides evenly into both terms, even if there’s a larger number that can divide both terms evenly.
Let's reduce the ratio 25:100.
We can see that 5 divides into 25 and 100, so we’ll try 5 out first.
25/5= 5
100/5 = 20
Our new ratio is 5:20.
Now we see that both 5 and 20 can be divided by 5 again.
5/5=1 20/5=4
The reduced ratio is 1:4.
We check that we can’t divide any more numbers into both terms other than 1, so 1:4 is our ratio written in lowest terms.
The greatest common denominator in this example is 25 because that number divides evenly into 25 and 100. But it may be easier to reduce the ratio into lowest terms in several steps.