# Margin of error for mean of group (when mean of each individual can't be calculated)

I am trying to compute the margin of error of a mean of a group.

Suppose a have a population of 50 workers and I want to know how much I'm paying as a whole in salary for each sale they perform (salary per sale). The problem is I only have data from four workers (simply, randomly chosen) and I want to use the data from these four to get an estimate from all 50. Here is the data:

Worker 1 = 50k , 1 sale -> 50k per sale;

Worker 2 = 100k , 3 sales -> 33k per sale;

Worker 3 = 150k, 5 sales -> 30k per sale;

Worker 4 = 75k, 0 sales -> n/a;

Total= 375k, 9 sales -> 42k per sale

I also have the salary data for the other 96 workers (just not their number of sales).