CCSS.Math.Content.5.NBT.A.2
The standard
Explain patterns in the number of zeros of the product when multiplying a number by powers of 10, and explain patterns in the placement of the decimal point when a decimal is multiplied or divided by a power of 10. Use whole-number exponents to denote powers of 10.
Common Core State Standards for Mathematics · Number and Operations in Base Ten
What this standard means
Students need to see that multiplying by 10, 100, or 1,000 makes a number ten, one hundred, or one thousand times as large. Dividing by those powers makes it smaller. They should write powers of 10 with exponents and connect 10³ to 1,000, not treat it as 10 times 3.
Mastery looks like explaining the pattern, not just moving the decimal. Students can predict 4.7 × 10² and 4.7 ÷ 10² and justify it with place value. Common trouble spots are adding zeros to decimals, moving the decimal the wrong way, and confusing the exponent with the number of zeros in every situation.
Ways to teach it
- Use a place value chart and digit cards to shift 3.26 left or right when multiplying and dividing by 10, 100, and 1,000.
- Ask students to explain why 5.4 × 100 is 540, but 5.4 + 100 is not related to that pattern.
- Give five problems mixing ×10, ×10², ÷10, and ÷10³, then ask for one written explanation of the decimal movement.
- Have students convert measurements, such as 2.5 meters to centimeters and 450 centimeters to meters, using powers of 10.
Plan a lesson for CCSS.Math.Content.5.NBT.A.2
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Related standards
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- CCSS.Math.Content.5.NBT.A.1
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