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1st Grade Math
12. 1.NBT.C.4
12.2 Adding digits up to 100
Adding Digits Up to 100
Build confidence with 2 digit addition by learning to line up tens and ones, add each column, and regroup when a column totals more than nine.
What You'll Learn
Split each two digit number into tens and ones before adding, such as writing 47 as 4 tens and 7 ones.
Add the ones column first, then the tens column, keeping digits lined up by place value.
Regroup ten ones into 1 ten whenever the ones column totals \( 10 \) or more, carrying that ten into the tens column.
Check that a sum like \( 47 + 36 = 83 \) makes sense by estimating with rounded numbers first.
Recognize when a problem needs no regrouping, such as \( 23 + 45 = 68 \), versus when it does.
Apply the same tens and ones method consistently, whether numbers are written horizontally or stacked.
What You'll Practice
1
Adding two numbers with sums up to 100
2
Finding missing numbers to complete addition statements
3
Solving vertical addition problems
Why This Matters
Adding numbers up to 100 is essential for everyday math like counting money, measuring ingredients, and telling time. This skill builds the foundation for all future arithmetic, including subtraction, multiplication, and solving word problems.
This Unit Includes
Practice exercises
Learning resources
Skills
Addition
Place Value
Regrouping
Two-Digit Numbers
Mental Math

OH Curriculum Aligned