I am sorry that you found the interview to be a negative experience. You have not said why though. You say if you already have a job do not take time to go for the interview. Looking at the date of your review, I believe we were looking for people who could start fairly quicky as we had a training course scheduled around that time. I am guessing you were one of a few individuals who were not selected because you were already working and needed to give your current employer notice. Working that notice may have meant you couldn't attend the training course. From the description you give you were being interviewed for one of our full-time salaried positions for graduate trainees which is why no experience was required. However the question you have cited was to test your simple mental arithmetic skills as that is a calculation we have to make regularly during a sales pitch.