Can you join the society ?
Albert and Bernard just became friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates:
•May 15, May 16, May 19
•June 17, June 18
•July 14, July 16
•August 14, August 15, August 17
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
Albert: I don't know when Cheryl's birthday is, but I know that Bernard doesn't know too.
Bernard: At first I don't know when Cheryl's birthday is, but I know now.
Albert: Then I also know when Cheryl's birthday is.
Two people secretly picked a whole number from 0 to 30 inclusive. Each knows the other has done this.
A : "Is your number double mine ?"
B : "I don't know. Is your number double mine ?"
A : "I don't know. Is your number half mine ?"
B : "I don't know. Is your number half mine ?"
A : "I don't know."
B : "I know your number"
11 22
12 24
14 28
15 30
20 30
22 33
24 ?