This is NOT a probability problem

Discrete Mathematics Level pending

There's 20 identical balls in weight and shape and texture. 10 of these balls are colored blue and the rest is red. Those balls are in a room dark enough so you can see the ball easily except it's color. Let's say that the outside of that room has enough light to see the ball color, so you must go inside the room and then go outside to check the ball color. There's just a single door to go inside that room(the door is open of course). Now your current position is outside of the room. What is the minimum amount of times you must pass that room's door to get at least a pair of balls with the identical color OUTSIDE of that room, if everytime you go into that room you are not allowed to bring more than one ball outside, and you are not allowed to bring that ball back once it's outside of the room?

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