Such smol boi

Josh and Peter just became friends with Abby, and they want to know her birthday. Abby gives them a list of 10 possible dates.

September 15, September 16, September 19
October 17, October 18
November 14, November 16
December 14, December 15, December 17

Abby then tells Josh the month and Peter the day of her birthday.

Josh: I don't know when Abby's birthday is, but I know that Peter does not know too.
Peter: At first I don't know when Abby's birthday is, but I know now.
Josh: Then I also know when Abby's birthday is.

So when is Abby's birthday?

1
11
21
1211
111221
312211
13112221
1113213211
??????????????

Testing yo inteligencion lik pro.

(x/3-1/12)/(x/4+1/6)=(x/21-1/4)/(x/28-1/6)

I'ma plaing frum Undying lands m8. Frudo is here too. But heez noob.

Gandalf? whatcha doin' here? you should be with Frodo, not playing games on steam!