So when is Ivy’s birthday

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?