TOPIC 1 · GRADE 3
Addition and Regrouping
Compose hundreds, tens, and ones to add accurately and explain every regroup.
Grade 3 focus: Place value, estimation, regrouping, and the inverse relationship between addition and subtraction.
BIG IDEA
Addition combines quantities. Place-value units must stay aligned, and 10 units in one place can be composed as 1 unit in the place to its left.
INTERACTIVE MATH LAB
Build it. Change it. Explain it.
MATH LANGUAGE
- addend
- a number being added
- sum
- the result of addition
- regroup
- rename 10 smaller units as 1 larger unit
- estimate
- a nearby value used to judge reasonableness
REPRESENT IT
- base-ten blocks
- expanded form
- open number line
- vertical algorithm
STRATEGY STEPS
- 1Represent each addend with hundreds, tens, and ones.
- 2Add ones, then tens, then hundreds; compose a new unit whenever a place reaches 10.
- 3Estimate before calculating so an unreasonable answer is easy to notice.
- 4Check by subtracting one addend from the sum.
WATCH OUT
A regrouped 1 has the value of its new place. Above the tens column it means 1 ten, not 1 one.
TRY IT
Change both addends, predict whether ones or tens will regroup, then reveal one step at a time.
WORKED EXAMPLE
268 + 157
- Estimate: 270 + 160 is about 430.
- Ones: 8 + 7 = 15. Write 5 ones and compose 1 ten.
- Tens: 6 + 5 + 1 = 12 tens. Write 2 tens and compose 1 hundred.
- Hundreds: 2 + 1 + 1 = 4 hundreds. The sum is 425.