Exchange Ten Ones When Adding
Separate the two-digit addend into tens and ones.
About 15 minutes, plus any extended practice
Supplied materials
- Paper and a pencil; drawing and spoken explanations are welcome. An adult may read directions and options aloud.
- Supplied worked-case record: For 38+7, three tens and eight ones receive seven more ones.
- All quantities and shape descriptions are supplied in the worked example and questions; no purchase or personal information is needed.
Learn the idea
Adding a one-digit number to a two-digit number can make more than nine ones. Ten of those ones can be exchanged for a full ten. The exchange changes the grouping, not the quantity, so the total before and after regrouping is identical.
Separate the two-digit addend into tens and ones. Add the new ones, exchange a group of ten ones when needed, and recount tens and leftover ones. Verify by counting on from the starting number.
An exchanged ten still represents ten original ones. Do not keep ten ones in the ones column after also recording their new ten. Draw tens as bundles and ones as single marks.
- Draw tens as bundles and ones as single marks.
- Follow the worked example. Point to each number or shape feature and say what it tells you.
- Separate the two-digit addend into tens and ones.
- Try the question and then the three practice questions. Check your answers and explain any change you make.
See the method in action
For 38+7, three tens and eight ones receive seven more ones. Fifteen ones become one ten and five ones. The result is four tens and five ones, or 45. Counting seven steps from thirty-eight also reaches forty-five. An exchanged ten still represents ten original ones. Do not keep ten ones in the ones column after also recording their new ten. Draw tens as bundles and ones as single marks.
Check your reasoning
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Helpful tips
- An exchanged ten still represents ten original ones.
- Do not keep ten ones in the ones column after also recording their new ten.
See the answer and explanation
35
Combine the ones, then exchange ten ones for one additional ten. The result is 35.
Take it further
Find 56+8. Expected: 64, because fourteen ones become one ten and four ones.
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More practice: try new cases
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