 If we have n distinct objects, and we want to arrange them into sequences where we cannot repeat any of those objects, then there are n factorial different ways to arrange them. Let's consider an example where we have four coloured balls, red, green, blue and yellow. And we want to put them into a sequence based upon their colour. Then of course one possible sequence, one arrangement is, as we see, red, green, blue and yellow. But of course we could have a different arrangement where we swap the blue and yellow balls and get a different sequence. Or we can have red, blue, green and yellow. Still the first ball is red, we've moved the blue ball. And we can keep creating different sequences. In this case there are six possible sequences where the first ball is red. And now we can try sequences where, for example, the first ball is green, green, red, blue and yellow. And we keep trying all the arrangements. There are six possible arrangements when the first ball is green and similar with blue and also with yellow. So this all possible arrangements of those four coloured balls and the total number is 24. And it is from four factorial is 24.