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Z.1 Add three-digit numbers using break apart

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What is the break apart strategy?

The break apart strategy is a way to add numbers by separating one number into smaller parts. This makes it easier to work with hundreds, tens, and ones when adding three-digit numbers.

Example:
  • 236 + 124 → Break apart 124 into 100 + 20 + 4
  • Add step by step: 236 + 100 = 336, 336 + 20 = 356, 356 + 4 = 360
  • Final answer: 236 + 124 = 360
Note

Breaking apart helps you add in parts, instead of trying to solve the whole problem at once.

How do we break apart numbers?

To break apart numbers, separate the smaller number into hundreds, tens, and ones. Then add each part to the bigger number one step at a time.

Steps:
  • Start with 342 + 158
  • Break apart the smaller number: 158 = 100 + 50 + 8
  • Add in order: 342 + 100 = 442, 442 + 50 = 492, 492 + 8 = 500
  • Final answer: 342 + 158 = 500
Note

Always break apart the smaller number. This keeps your steps simpler and faster.

Why does breaking apart work?

Breaking apart works because numbers are built from hundreds, tens, and ones. Adding them in parts follows place value rules and keeps the work organized.

Example:
  • 215 + 132 → Break apart 132 = 100 + 30 + 2
  • 215 + 100 = 315
  • 315 + 30 = 345
  • 345 + 2 = 347
Note

This strategy makes big problems easier because you only add one place value at a time.

Using the break apart strategy in real life

We use breaking apart in real life when adding large amounts step by step, such as money, distances, or objects in groups.

Example:
  • You have 278 baseball cards. You buy 143 more.
  • Break apart 143 → 100 + 40 + 3
  • Add: 278 + 100 = 378, 378 + 40 = 418, 418 + 3 = 421
  • Total cards = 421
Note

Breaking apart helps with quick mental math when exact steps are needed in everyday situations.