199.5乘199.4减199.1乘199.8的简便计算

Question

199.5乘199.4减199.1乘199.8的简便计算

Answer 1

199.5×199.4﹣199.1×199.8
=﹙200﹣0.5﹚×﹙200﹣0.6﹚﹣﹙200﹣0.9﹚×﹙200﹣0.2﹚
=﹙200×200﹣200×0.5﹣200×0.6﹢0.5×0.6﹚﹣﹙200×200﹣200×0.9﹣200×0.2﹢0.9×0.2﹚
=200×200﹣200×0.5﹣200×0.6﹢0.5×0.6﹣200×200﹢200×0.9﹢200×0.2﹣0.9×0.2
=200×0.9﹢200×0.2﹣0.9×0.2﹣200×0.5﹣200×0.6﹢0.5×0.6
=200×﹙0.9﹢0.2﹣0.5﹣0.6﹚﹣0.9×0.2﹢0.5×0.6
=0.5×0.6﹣0.9×0.2
=0.3﹣0.18
=0.12