Stephen and Anna are working on the audit of Flower Enterprises, a regional distributor of floral bouquets and other decorations in the southwestern United States. The Chief Financial Officer of Flower Enterprises has advised that the variance in balances for accounts receivable is extremely wide, with some corporate clients maintaining large receivables balances, and other individual clients keeping smaller balances." Based on this information, which of the following sampling strategies are MOST likely to be adopted by the auditing firm?