Choosing Plus or Minus: Deciding Which Sign Matches the Story

Look for this idea outside of your lessons. A shopkeeper who adds when he should subtract will think he has more bread than he really has. Choosing right matters more than counting fast. This is worth learning because a right answer to the wrong question is still a wrong answer.

Watch for it today, and when you spot it, tell someone what you noticed and how you knew. Let us think about this slowly. Before you compute, decide which sign the story needs. Ask one question: did the group get bigger or smaller?

If more arrived, use plus. If some left, use minus. Say the story back in your own words first. Guessing the sign is the fastest way to get a wrong answer with perfectly good counting. Decide first, then count, and check that your answer makes sense for the story you heard. Try this check at the end.

Look at your answer and ask whether it fits the story. If four birds flew away from a group of six and your answer is ten, something is wrong, because the group should have shrunk. Answers that do not fit the story are worth a second look. Show your work to someone and explain it in your own words.