Last year Deparment Store x had a sales total for December that was 4 times the average (arithmetic mean) of the monthly sales totals for January through November. The sales total for December was what fraction of the sales total for the year?
December Sales = D
Arithmetic mean for Jan thourgh Nov=X,
sales total for Jan-Nov = 11X
Sales total for the year =11X+D
December sales total =4X