CCSS.Math.Content.2.NBT.B.5
The standard
Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.
Common Core State Standards for Mathematics · Number and Operations in Base Ten
What this standard means
Students need to add and subtract two-digit numbers within 100 without relying only on counting by ones. They should use tens and ones, break numbers apart, make a ten, use friendly numbers, and check subtraction with addition.
Mastery looks like quick, accurate work with a strategy they can explain. A student might solve 47 + 28 as 40 + 20 and 7 + 8, or solve 62 - 37 by counting up from 37 to 62. Common trouble spots are regrouping, mixing up tens and ones, and using a strategy that does not fit the numbers.
Ways to teach it
- Give students base-ten blocks and have them model 46 + 29, trade ten ones for a ten, then record the equation.
- Ask students to solve 83 - 48 two ways and write which strategy felt easier and why.
- Show 56 + 27, 90 - 34, and 72 - 19 on the board, then collect answers on sticky notes.
- Use a class store price list and ask partners to find totals and change for two items under one dollar.
Plan a lesson for CCSS.Math.Content.2.NBT.B.5
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