Calculate webform droplist values with jquery

We need to calculate a score based on the webform input of 5 dropdownlists. Each dropdownlist has 6 options and a default 'please select'. The first option has a score of 0 so up to a score of 5. We need the sum of all scores and divided by the number of dropdownlists a user has given a value. So if a user filled in all 5, we devide by 5. If a user left 2 on the 'please select' default, we divide by 3. The average score is rounded up. So we get a nice final score between 0 and 5. This needs to be displayed in a textfield. Should be an easy job for someone who knows their code! See attachment.