Cogito
Grade 2 Math · Chapter 5 · Lesson 5
Breaking a Hundred Apart
Not enough tens? Open a hundred.
10 problems · about 14 minutes · 2.NBT.B.7, 2.NBT.B.9
What this lesson teaches
The child unbundles one hundred into ten tens and subtracts when the tens are short.
- If there are not enough tens, break a hundred open.
- One hundred becomes ten tens.
- The amount stays exactly the same.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Subtracting Within 1,000: 758 − 326 = ?
Answer 432
Why 758 − 326 = 432.
Review — Making a New Hundred: 275 + 168 = ?
Answer 443
Why 275 + 168 = 443.
Warm Up
Straightforward practice. Get the method working first.
4 problems635 − 172 = ?
Answer 463
Why 635 − 172 = 463.
Breaking a hundred gives you how many tens?
Answer 10
Why One hundred is ten tens.
526 − 183 = ?
Answer 343
Why Only 2 tens. Break a hundred.
748 − 265 = ?
Answer 483
Why 4 tens cannot lose 6.
Build It Up
The same ideas with more to keep track of.
2 problems3 hundreds and 14 tens is which number?
Answer 440
Why 300 and 140.
859 − 327 = ?
Answer 532
Why No breaking needed here.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsAnother Way to Show It: 2 hundreds, 15 tens and 4 ones is which number?
Answer 354
Why 2 hundreds and 15 tens is 350, plus 4 makes 354.
The Shop: A shop had 634 items and sold 281. How many are left?
Answer 353 items
Why 634 − 281 = 353.