Brain Teasers
I Know He Knows; You Don't Know I Don't
-I walk into a room
-I know everyone who knows who was first in the room
-You walk in after me
-You don't know everyone who knows who was first in the room
How many people are now in the room?
-I know everyone who knows who was first in the room
-You walk in after me
-You don't know everyone who knows who was first in the room
How many people are now in the room?
Hint
Try to figure out how many were to start then add 2.Answer
There are 4 in the roomAt least 2 people enter the room; me and you.
If 1 person were in the room to start, I would know who was first in the room, as well as everyone who who knows who was first in the room.
Therefore, if you walk in with 1 other person & I, you know we both know who was first.
If there were 0, same story.
If there are 3 or more, I don't know who knows who was first in the room, because only 2 of them know.
Therefore, the answer is 4.
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