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Subtraction can be used to model three situations:
- Separation - Where you have a total count of objects, a count of objects from part of the group, and you want to find out how many objects are left.
- Comparison - Where you have a count for two groups of objects and want to find the difference between the two groups.
- Part-Whole - Where you know how many objects you had and how many objects are left and you want to know the total.
You just ordered 100 copies of a best selling book. You've sold 32 copies so far today. Someone calls you on the phone to ask about the book. How many copies should you tell them are left?
It is the end of the first day of selling the book. 32 copies were sold in the morning but only 26 copies were sold in the afternoon. How many more copies were sold in the morning than the afternoon?
You received 100 books. You sold 32 copies in the morning and 26 copies in the afternoon. How many books do you have left?
In between customers you're reading this new best selling book also. The book has 300 pages and today you read 112. How many pages do you need to read tonight if you want to finish the book?
You start the day with 100 books and by the end of the day you have 52 left. How many did you sell?