So, for example, if you wanted the average to be 5.00, accurate to 2 decimal places, then you would want the actual calculated average to be a minimum of 4.995.
If we let x be the number of additional scores of 5 that need to be added to the current survey, then you would write the following equation:
(total scores + 5x) / (number of scores + x) = 4.995
So, for the survey totals given in your original posting, the total of the scores was 48, and the number of scores was 12. This would give the following:
(48 + 5x) / (12 + x) = 4.995
You would solve this for x by multiplying both sides by (12 + x) to get:
48 + 5x = 4.995(12 + x)
48 + 5x = 59.94 + 4.995x
5x - 4.995x = 59.94 - 48
0.005x = 11.94
Dividing both sides by 0.005 then gives:
x = 2388
So you would need to add an additional 2388 surveys, all of which would have to be scored as a 5, in order to raise the average to 4.995, which would be 5.00 if you rounded off to two decimal places.
I hope this helps. Please feel free to ask if you have any additional questions about this.