there are 5 red marbles, 3 blue and 4 black of different sizes. In how many ways they can be put in a row so that the marbles of same color are always together?

There are 3! ways to arrange the three colors.

Within each color, there are 5!,3!,4! ways to arrange the different marbles.

So, there are 3!5!3!4! = 103680 ways to arrange the marbles as specified.