Study guide: Use Efficient Strategies Within Twenty
Use ten, doubles, friendly groupings, and related addition to calculate.
Ideas to explain in your own words
- Ten is a useful landmark when adding across it.
- A double joins two equal amounts.
- Three amounts can be grouped in a useful order because their total does not depend on which pair is added first.
- Subtracting across ten can be split into a first removal that reaches ten and a second removal of the remainder.
Useful vocabulary
- double
- A sum of two equal amounts.
- make ten
- Break an addend so part of it completes ten.
Watch your reasoning
- After filling ten, add the leftover part, not the full addend again.
- A near double includes one more than the exact double.
- Changing the grouping must not lose or repeat an addend.
- Do not remove the entire subtrahend again after reaching ten.
A worked review example
For 9+5, nine needs one to reach ten. Split five into one and four: 9+1+4=10+4=14. The added parts still total five. The ten-frame model shows a full frame with four extra marks, matching fourteen. Only use enough of the second addend to reach ten. After filling ten, add the leftover part, not the full addend again. Use one ten-frame plus extra marks to show the split.
Make a practice plan
- Make a Ten Before Adding the Rest: Find 7+6. Expected: 7+3+3=13.
- Use a Known Double for a Near Double: Find 8+9. Expected: 16+1=17.
- Group Three Addends into an Easier Sum: Find 3+8+7. Expected: 3+7+8=18.
- Subtract in Two Parts Through Ten: Find 16−9. Expected: 16−6−3=7.