The bigger the denominator, the smaller the fraction. We could go through finding the common denominator, but if you just remember this simple rule, it's easier for this problem, seeing as how the numerators are all the same. If the numerators are different, be sure to find a common denominator to check your work.
The bigger the denominator, the smaller the fraction, because it splits up the whole into more pieces.
This means that in the group of three fractions, 3/8, 3/7, and 3/9, 3/9 is going to be the least, because 9 is the largest denominator of the three.
So, from least to greatest, the fractions go 3/9, 3/8, 3/7.
