请问这一道很简单的sat数学题A clerk accidentally threw a valuable document into one of 90 trash cans.It is equally likely that the document is in any of these 90trash cans.If exactly 15 of these 90 trash cans are blue,what is the probability that the document will be in a blue trash can?我觉得答案是1/15但是参考答案是1/6为什么呢
问题描述：
请问这一道很简单的sat数学题
A clerk accidentally threw a valuable document into one of 90 trash cans.It is equally likely that the document is in any of these 90trash cans.If exactly 15 of these 90 trash cans are blue,what is the probability that the document will be in a blue trash can?
我觉得答案是1/15但是参考答案是1/6
为什么呢
答
是 15/90 啊.
因为 是在90个里面有15个蓝盘子,简单一比就好啊.
如果是你的答案,那你没有考虑盘子的总数.如果总数是100个,你的答案还是这样,但是实际上应该是15/100.想想也知道比例会小.