Expert mathematicians sought... Headache & a half...

I will endevour to explain this as best as I can... Thanks for your help in advance everyone! I work in an industry that analyses surveys sent from customers. Surveys can only be positive or negative. (Simple as that really).

Now we have a site target to reach 90% positive. As a constant variable it's pretty easy(ish) calculation: For every negative survey you need 9 more positives -- so the calculation is something along the lines of having the computer calculate how many negatives (number of positives / number of total surveys), multiply that number by 9 and subtract the number of positives recieved to see how many more you need...

Example: Guy has 11 surveys. 4 are negative. He's gonna need 36 total positive surveys to reach 90%. He has 11-4=7 positives, which leaves him with 29 more surveys to get to reach the constant target.

BUT... Owing to my stupididty in the quest for better - I want to know how many more surveys are needed to meet the program average (and the calculation for such)...

So, let's assume the site average is 91.66667% In order to reach the site average, 'guy' in my example actually needs 44 out of 48 to reach this goal... But how to have excel calculate how to get this number based on the contstant changing variable (the target)???

The data is used to try and steer the employees to reach > average... I'm not opposed to having excel round up numbers in order to create a target but I just can't think any more how the best way to tackle the problem...

All suggestions (and example spreadsheets???) welcome :)

Thanks everyone!

D