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Question
Gary and Henry just become friends with Ivy, and they want to know when her birthday is. Ivy gives them a list of 10 possible dates.
January 5 January 6 January 9
February 7 February 8
March 4 March 6
April 4 April 5 April 7
Ivy then tells Gary and Henry separately the month and the day of her birthday respectively.
Gary: I don’t know when Ivy’s birthday is, but I know that Henry does not know too.
Henry: At first I don’t know when Ivy’s birthday is, but I know now.
Gary: Then I also know when Ivy’s birthday is.
So when is Ivy’s birthday?
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原文地址：http://www.cnblogs.com/ganting/p/4500503.html
