Question

There are some cubes in a bag. The cubes are either red or black.

''If you take a cube out of the bag, the probability that it will be red is 1/5

''What is the probability that the cube will be black?''
''A pupil takes one cube out of the bag. It is red. What is the smallest number of black cubes there could be in a bag?''
''Then a pupil takes another cube out of the bag. It is also red. From this new information, what is the smallest number of black cubes there could be in the bag?''