What is happening
You arrive at a library trolley that has to go back to the shelf full.
The trolley cannot go back half empty. There are 3 books on it, and the shelf slot it belongs to takes 9.
Counting on to nineRunning
Books on the trolley
12.2books
Slot takes
9books
Sequence steps. Books added at 9 books. Books on the trolley 12.2 books, Slot takes 9 books. Currently books on the trolley is over by 3.2 books.
What has to balance