Answer:
The answer is that the last marble is red.
Step-by-step explanation:
The answer is that the last marble is red.
We can justify this answer by denial:
For the last marble to be blue, at some stage in the extraction of marbles there must have been n blue marbles and one last red marble.
To remove that red marble, it has to be extracted in one of the following rounds.
If the last red marble is removed, the other marble extracted will be a blue one. Since the marbles extracted are of different color, according to the rules, a red marble must be incorporated into the bag.
So the amount of red marbles in the bag cannot decrease to less than one.
For this reason the last marble is red.
