I have a question why the solution of this is o.3 (3) and not 1/3, if we only have a chance between 3?

Hey Mariana,  The idea here was mostly to see if you were paying attention to what the appropriate representation of probabilities is.  All the answers provided hold the same numeric value. The only difference is one is percentages, once is a fraction, one uses odds and the last one uses a number value between 0 and 1.  Since numeric values between 0 and 1 are the norm, this is why this answer is correct.  Best,  365 Vik   P.S. Using fractions when computing values is perfectly fine. The goal here is to make you understand that computers represent probabilities with numbers between 0 and 1, rather than percentages.