CCSS.Math.Content.2.NBT.B.6
The standard
Add up to four two-digit numbers 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 add three or four two-digit numbers by grouping tens and ones, making friendly numbers, and using partial sums. They should explain why a strategy works, not just stack numbers and hope. They may use drawings, base-ten blocks, number lines, or equations.
Mastery looks like choosing an efficient strategy, keeping track of all addends, regrouping ones into tens when needed, and checking for reasonableness. Common trouble spots are losing a number, mixing tens and ones, writing messy partial sums, or treating 27 + 35 as 20 + 30 + 7 + 35.
Ways to teach it
- Have students use base-ten blocks to build 24, 18, 31, and 12, then combine ones, trade for tens, and record the sum.
- Ask, “Which numbers would you add first in 36 + 14 + 27 + 23, and why?” then have students compare strategies.
- Give three problems on a sticky note, including one four-addend problem, and ask students to show tens and ones in their work.
- Use a class party snack list with prices like 24, 35, 18, and 22 cents, then have students find the total cost.
Plan a lesson for CCSS.Math.Content.2.NBT.B.6
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