请问这一道很简单的sat数学题A clerk accidentally threw a valuable documen
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