3.25, 29/8, 3.52, 31/9

We divide out the fractions to make them into decimals:

          3.625               3.444  
29/8 = 8)29.000     31/9 = 9)31.000
         24                  27
          5 0                 4 0
          4 8                 3 6
            20                  40
            16                  36 
             40                  40
             40                  36
              0                   4

Then we annex a 0 on the ends of 3.25 and 3.52 making them 
3.250 and 3.520

Then we have 5 decimals taken to the same number of decimal 
places:

3.250, 3.625, 3.520, 3.444

Now it's easy to tell now how to arrange them smallest to largest.
Just compare the decimal parts

3.250, 3.444, 3.520, 3.625

or as they were originally:

3.25, 31/9, 3.52, 29/8

Edwin