Suppose c0 is the overhead cost (such as maintaining office space) and ch is the cost associated with each observation from the h-th stratum (for h = 1, ..., h). In this case, the total cost will be c = c0 x Σ h=1 to nhch. Then, if we are interested in estimating the unknown population mean yu by ystr, derive the optimal allocation of strata sample sizes by minimizing var (ystr) for a specified total cost of c (set as the budget for the survey).