Subtraction as a Missing Addend: What Goes with This to Make That

Think about where you have seen this before. A cashier making change counts up from the price to the bill. She never counts backward, because counting up is faster and safer. This is worth learning because seeing subtraction as missing addition makes hard facts much easier.

Watch for it today, and when you spot it, tell someone what you noticed and how you knew. Ask yourself where else the same idea might be hiding, then go and look.

Take a deep breath and look at this. Every subtraction problem is really an addition question in disguise. Think of 13 minus 8. Instead of taking away, ask what goes with eight to make thirteen. Count up from eight: nine, ten, eleven, twelve, thirteen.

Five steps. So the answer is five. Many people find counting up easier than counting back, especially when the numbers are close together. Both give the same true answer.

Here is why this matters so much. Counting back seven steps invites mistakes, but counting up from a number is steady and short when the numbers are close. Choose counting up whenever the two numbers sit near each other on the number line. When you get it right, say thank You to God, who gave you that thinking mind.