I have 3 bags of marbles

1 bag is labeled blue; 2nd bag is labeled red; 3rd bag is labeled blue & red

all the bags are mismarked

your job is to take on marble from 1 bag look at it and correctly label all the bags

the answer has to written out as to how to label them correctly

The 3rd bag is labeled "blue and red" and you know this labelling is incorrect. Thus the 3rd bag has either all blue or all red marbles in it. Take a marble from this bag. Suppose it is blue. At this point you know;