Study guide: Explain Regrouping and Two-Step Stories
Regroup in addition and subtraction, adjust mental sums, and keep two story changes separate.
Ideas to explain in your own words
- Multi-digit addition joins matching units: ones with ones, tens with tens, hundreds with hundreds.
- A subtraction can require more ones than the starting ones place shows.
- A nearby multiple of ten can simplify addition.
- A two-step story has an intermediate amount after its first change.
Useful vocabulary
- regrouping
- Renaming a quantity using different base-ten groups.
- intermediate total
- The amount after the first step but before the next.
Watch your reasoning
- Regrouping preserves value; it does not create an extra amount.
- Check subtraction by adding the difference and the removed amount.
- If you rounded an addend up, correct the sum downward.
- A result after the first change is not the final answer.
A worked review example
For 156+127, ones total thirteen: one ten and three ones. Tens then total eight, including the exchanged ten. Hundreds total two. The result is 283. The extra ten came from the thirteen ones, so it must not remain counted in the ones column. Add the exchanged group into its new place. Regrouping preserves value; it does not create an extra amount. Use a place-value chart and show every exchange with an arrow.
Make a practice plan
- Add Hundreds with an Exchange: Find 278+146. Expected: 424.
- Rename a Ten Before Subtracting Ones: Find 83−46. Expected: 37; seven tens and thirteen ones before removal.
- Adjust a Mental Sum Around a Friendly Ten: Find 68+19. Expected: 68+20−1=87.
- Track Two Different Changes in a Story: Start with 72, remove 19, then add 24. Expected: 77.