Cogito
Grade 3 Math · Chapter 2 · Lesson 5
Subtracting Within 1,000 Fluently
Break a unit open when you need to.
10 problems · about 14 minutes · 3.NBT.A.2
What this lesson teaches
The child subtracts three-digit numbers within 1,000 fluently, unbundling where needed.
- Check every column before you start.
- Break a hundred or a ten when a column runs short.
- Check the answer by adding it back.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Adding Within 1,000 Fluently: 385 + 247 = ?
Answer 632
Why 385 + 247 = 632.
Review — Estimating Sums and Differences: Estimate 406 + 195 to the nearest hundred.
Answer 600
Why 400 + 200 = 600.
Warm Up
Straightforward practice. Get the method working first.
4 problems905 − 348 = ?
Answer 557
Why 905 − 348 = 557.
How do you check a subtraction?
Answer Add the answer to what was taken away.
Why It should return the number you started with.
624 − 358 = ?
Answer 266
Why Break a ten and a hundred.
700 − 265 = ?
Answer 435
Why Break twice.
Build It Up
The same ideas with more to keep track of.
2 problems486 − 253 = ?
Answer 233
Why No breaking needed.
Check it: 233 + 253 = ?
Answer 486
Why It should return to 486.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Collection: A collection of 613 stamps loses 248. How many are left?
Answer 365 stamps
Why 613 − 248 = 365.
The Target: A target of 800 has 342 done. How many are left?
Answer 458 left
Why 800 − 342 = 458.