Sat数学题求解释和过程At a department store,3/5of the items are discou

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?