Don't know what the book says, my personal opinion is this: first find the simplest ratio of 60 and 72, keep dividing, and finally simplify to 5:6, so that the smallest common multiple of 60 and 72 is 60 multiplied by 6 (or 72 multiplied by 5)=360, and as for the largest common multiple, there doesn't seem to be any, right? And so on for other numbers ------