This is why people drop out of school

It isn't only about what you say, but how you say it.

Generally, if the fraction does not convert to a finite number of decimal places, the fraction form is preferred. For instance, 1/8 = 0.125, so either may be fine; however, 1/3 = 0.33333... so the 1/3 is best for most applications. Also, if you are dealing with probabilities, the denominator is sometimes left as the total number of possible outcomes, even if it can be reduced. This is for information density, as it conveys both the probability of a specific outcome occurring and retains the information about how many overall outcomes there are. As an example, the chance of drawing a king from a complete deck of cards is 4/52, which is also 1/13 or .076923... but, by only reporting a reduced fraction or decimal, you lose some information about the total number of cards, as well as the total number of kings.

I know, but i got the question completely wrong because of it

Did you ask your professor to look at your test? I used to be a TA and we would give students credit for things like that. They can override your score that the computer assigned.