Sat数学题求解释和过程

题目

Sat数学题求解释和过程
At a department store,3/5of the items are discounted by 50 percent, 1/5of the items are discounted by 70 percent, 1/10 of the items are discounted by 80 percent, and all other items are not discounted. If one item is to be chosen at random, what is the propability that the item is discounted by either 50 percent or 70 percent?

答案

在百货公司,3/5的商品打5折,1/5的商品打3折（折让7折）.1/10的商品打2折,其余的是不打折的.假设一个商品被随机选中,那么这个商品打5折或者是3折的概率有多大?
5折：3/5
3折：1/5
5折或者是3折的概率 3/5+1/5=4/ 5