Column taking away

What this chapter teaches

Take away from the right. When a top digit is too small, exchange 1 ten for 10 ones, or 1 hundred for 10 tens. Add back to check. A common mistake is taking the smaller digit from the bigger in each column.

Three questions to ask

There is no one right wording. Listen for the idea.

1. What do you do when the top digit is smaller than the bottom digit?
2. How could you check that 403 − 167 = 236 without doing it again?
3. What is wrong with answering 364 for 403 − 167, and how can you tell?

After the chapter, the learner can

• Take away 3 digit numbers in columns, exchanging when you need to
• Take away across a zero, as in 403 − 167