When dealing with math problems it is common to give the most exact answers. In fractions, 1/3 is more exact then 0.3 since 1/3=0.3333.... 

Another rule in math is to reduce your answer to the simplest representation possible, meaning 8/6 must be 4/3 (as 4/3 cannot be reduced any further). 

When applied to areas like physics or chemistry it is more common to use decimals with the right significance (If that doesn't mean anything to you yet no problem, you'll learn that later on!).