Five workers have been hired to complete a job. If one additional worker is hired, they could complete the job $15$ days earlier. If the job needs to be completed $40$ days earlier, how many additional workers should be hired?
5 workers * x days <====== are needed to complete the job
Add 1 worker and 15 less days are required :
6 workers * (x-15) = 5 * x
6x - 90 = 5x
x =90 days for 5 workers to complete the job
so 5 workers * 90 days = 450 worker days required for the job
450 worker days / w = 90 - 40 days
w = workers needed = 450 / 50 = 9 workers needed or 4 additional workers above the original number of 5