when you write 0.33333333 in a calculator and convert it to fraction using the a b/c button you should get 1/3 as an answer
another method is
Step 1: Write down the decimal divided by 1
Step 2: Multiply both top and bottom by 10 for every number after the decimal point. (For example, if there are two numbers after the decimal point, then use 100, if there are three then use 1000, etc.)