hi bro Ok here is the explanation. Consider the graph paper. The small box in the graph paper can accomade the 3 particles. When the particles number is 4 all the particles move to both x and y boxes so that it is empty.if the large number of sand is dropped on the box what will be distribution of the sand. If you droped the 100 sand (particles) and there are 50 boxes then we have to find out the no of sand particles in every boxes. Remember one box can't contain more than 3 particles. Thanks