Which number produces a rational number when added to 0.25?

For this case, the first thing you should know is the definition of a rational number.
 A rational number is that you can write as an exact fraction.
 For example,
 0.25 = 1/4
 We have then that:
 2/9 + 1/4 = ((2 * 4) + (1 * 9)) / (9 * 4) = (8 + 9) / (36) = 15/36 = 5/12
 5/12 is a rational number.
 
 A number that produces a ration number when added to 0.25 is:
 2/9 (option C)