采购金额 = (销售成本) + (期望期末存货) – (期望期初存货)，销售成本= (100% – 毛利率)(销售)
11月的销售成本 = (100% - 35%)($58,000) = (0.65)($58,000) = $37,700
11月的期末存货 = (30%)(12月的销售成本) = (0.3)(0.65)($74,000) = $14,430
11月的期初成本 = (30%)(11月的销售成本) = (0.3)($37,700) = $11,310
因此，11月的采购金额 = $37,700 + $14,430 – $11,310 = $40,820
