While looking at an old program listing (Chateau Gaillard by Tim Hartnell) I came upon this:
This struck me as odd: why not just use X=RND*18?
It turns out that the first example heavily biases the random number toward the middle of the range. There are many more ways to get numbers around the middle than there are ways to get numbers at the low and high extremes. If it is INT(RND*6)+INT(RND*6)+INT(RND*6) there is only 1 way to get a 0 or 15; 3 ways to get a 1 or 14; 6 ways to get a 2 or 13; 10 ways to get a 3 or 12, and so on.