A bag has 6695 blue marbles and 6696 red marbles. We repeatedly remove 2 marbles from the bag. If the two chosen marbles are of the same color then we put 1 new red marble in the bag (after removing the 2 chosen marbles). If the two marbles are of different colors then we put one new blue marble in the bag. What will be the color of the last marble in the bag

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  blue

Step-by-step explanation:

If two red marbles are removed, 1 red is returned. The number of reds is reduced by 1, and the number of blues is unchanged.

If two blue marbles are removed, 1 red is returned. The number of reds is increased by 1, and the number of blues is decreased by 2.

If one of each is removed, one blue is returned. The number of reds is reduced by 1, and the number of blues is unchanged.

So, at each step, the number of blue marbles is unchanged or reduced by 2. That is, it only changes by an even number. The number of blues is initially odd, so can never reach zero.

The last marble in the bag is blue.