Finding the Missing Addend in Sentences Like 8 Plus Blank Equals 12

Look for this idea outside of your lessons. Missing amounts are everywhere. A cook knows the recipe needs twelve eggs and eight are in the bowl. She needs no reminder of what to do. This is worth learning because missing number problems are the beginning of algebra. Watch for it today, and when you spot it, tell someone what you noticed and how you knew.

Let us think about this slowly. A blank means a number is hiding. In 8 plus blank equals 12, you know one part and the whole. Count up from eight to twelve: nine, ten, eleven, twelve. Four steps, so four fills the blank.

Check by adding: eight plus four is twelve. The blank is not scary. It is simply a missing part, and you already know how to hunt for missing parts.

Watch out for this. Some people see a blank and add the two numbers they can see, giving twenty for 8 plus blank equals 12. But twelve is the whole, so the blank must be smaller than twelve. Ask which number is the whole before doing anything. Show your work to someone and explain it in your own words.