35% wouldn't be an improper fraction - it would be a proper fraction. 35/100, or 7/20 is the proper fraction answer. An improper fraction is where you have a larger number as a numerator and a smaller number as the denominator, such as 100/35.
0.35 is a fraction. It is a fraction in decimal form rather than in the form of a ratio. However, that does not stop it being a fraction. Its rational equivalent is 35/100 which can be simplified, if required.