CCSS.Math.Content.3.NBT.A.3
The standard
Multiply one-digit whole numbers by multiples of 10 in the range 10—90 (e.g., 9 × 80, 5 × 60) using strategies based on place value and properties of operations.
Common Core State Standards for Mathematics · Number and Operations in Base Ten
What this standard means
Students need to multiply a one-digit number by 10, 20, 30, and so on through 90. They should see 6 x 40 as 6 groups of 4 tens, which is 24 tens, or 240. They are using place value, not just adding a zero.
Mastery looks like explaining the tens reasoning with words, drawings, or equations, such as 7 x 80 = 7 x 8 tens = 56 tens = 560. Students often get stuck by treating the zero as a trick, or by mixing up 6 x 40 with 60 x 4 without explaining why it works.
Ways to teach it
- Build 4 x 30 with base-ten rods, record it as 4 groups of 3 tens, then write 12 tens equals 120.
- Ask students to explain which is clearer, 5 x 70 equals 35 tens or 5 x 70 equals 350 because you add zero.
- Give four problems on a sticky note, 3 x 20, 8 x 50, 6 x 90, and 7 x 40, with one sentence explaining one answer.
- Use a classroom supply order, 6 packs with 30 pencils each, and have students find the total using tens reasoning.
Plan a lesson for CCSS.Math.Content.3.NBT.A.3
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Related standards
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- CCSS.Math.Content.1.NBT.C.4
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- CCSS.Math.Content.4.NBT.B.5
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- CCSS.Math.Content.1.NBT.C.6
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