### 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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