请教一个概念和一道PS

sherry

1. princeton上一道：m为奇数, m is not a perfect square, 其中perfect square是什么意思呀？

2. high-gmat上一道：if X and Y are sets of integers, X # Y denotes the set of integers that belong to set X or set Y, but not both. if X consists of 10 integers, Y consists of 18 integers, and 6 of the integers are in both X and Y, the X # Y consists of how many integers? 答案有：6 16 22 30 174
我选22，可答案为16，为什么？

sherry

哎，恍然大悟。thank you joywzy!

joywzy

sherry;

要特别注意英文题中表达式可能与我们常做的不同,一定要看清,千万别出错.如果会做又做错了,真是要气死了!

改掉粗心的毛病,与你共勉!

joywzy

1,完全平方数

2,是你粗心了,呵呵,怎么跟我一样啊?
, X # Y denotes the set of integers that belong to set X or set Y, but not both. 22-6=16.