2/5, 9/10, 7/5, 19/10, 12/5
find the common difference between the terms of the following arithmetic sequence.

Those sequence could be rewritten as :

4/10   , 9/10    , 14/10   , 19/10  , 24/10

From that sequence, we can see that the difference is 5/10 or  a 1/2

hope this helps