3/5 is already expressed as a fraction. It indicates how many parts of a whole we have, in this case, 3 out of 5 equal parts.
To further explain, a fraction consists of a numerator (the top number) and a denominator (the bottom number). In the fraction 3/5, 3 is the numerator, representing the number of parts we have, and 5 is the denominator, indicating the total number of equal parts in the whole. Thus, 3/5 means you have three parts out of a total of five.