Hello mathaddictImagine that the boxes are arranged in a line in front of you, and you've then got to arrange the balls, one in each box so that the colours match. There's only one possible way to do this.

Now figure out how many different ways there are altogether of putting the balls into the boxes, one in each. There are 4 ways of putting a ball into the first box, 3 ways for the second, and so on. So how many arrangements are possible altogether? Only one of these is correct. So what's the probability of that? So what's the probability that it's not correct?

Grandad