There is an urn with red and orange balls. The balls are of the same size and weight, only differentiated by their color. You do not know the number of balls in the urn. You take out two random balls from the urn at a time and replace with one ball as below.

i) If both the balls are of red color, you put one red ball back in the urn.

ii) If both the balls are of orange color, you again put one red ball back in the urn (there are spare red balls in case you fall short).

iii) If the balls are of different colors (1 red and 1 orange), you put one orange ball back in the urn.

You stop when you have only one ball left in the urn. What is the color of the last ball in the urn and why? If your answer has conditions, please call out the conditions.

  • 2
    $\begingroup$ Oof, @Deusovi. I'd just figured out the answer and was 2 seconds away from posting it :-) $\endgroup$ Commented Jul 27, 2020 at 6:51


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