Subtract Whole Tens from Whole Tens

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 80−30, eight tens lose three tens.
• All quantities and shape descriptions are supplied in the worked example and questions; no purchase or personal information is needed.

Learn the idea

When both amounts are multiples of ten, you can subtract their counts of tens. The answer still needs its value in ones, so multiply the remaining tens count by ten. This makes a group model useful without drawing many separate objects.

Represent both supplied amounts as tens groups. Remove the stated number of groups, count the tens left, and name their whole-number value. Check by adding the removed tens back to the result.

Five tens means fifty objects. Do not report only the number of tens when the question asks for the whole amount. Draw one bundle for each full ten and label every bundle 10.

1. Draw one bundle for each full ten and label every bundle 10.
2. Follow the worked example. Point to each number or shape feature and say what it tells you.
3. Represent both supplied amounts as tens groups.
4. Try the question and then the three practice questions. Check your answers and explain any change you make.

Check your reasoning

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Take it further

Find 90−50. Expected: four tens, or 40.

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