Cogito
Grade 2 Math · Chapter 5 · Lesson 3
Making a New Hundred
When the tens fill up, bundle them.
10 problems · about 13 minutes · 2.NBT.B.7
What this lesson teaches
The child adds within 1,000 where the tens compose a new hundred.
- Ten tens bundle into one hundred.
- Do the ones first, then the tens.
- A sum can need two bundles.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Adding Within 1,000: 341 + 236 = ?
Answer 577
Why 341 + 236 = 577.
Review — Adding and Subtracting Hundreds: 400 + 500 = ?
Answer 900
Why 400 + 500 = 900.
Warm Up
Straightforward practice. Get the method working first.
4 problems275 + 168 = ?
Answer 443
Why 275 + 168 = 443.
Ten tens bundle into what?
Answer One hundred.
Why Ten tens make one hundred.
350 + 280 = ?
Answer 630
Why 13 tens.
164 + 172 = ?
Answer 336
Why 6 and 7 tens.
Build It Up
The same ideas with more to keep track of.
2 problems247 + 158 = ?
Answer 405
Why A new ten, then a new hundred.
390 + 240 = ?
Answer 630
Why 13 tens again.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTwo Crowds: 260 people came in the morning and 170 in the afternoon. How many in all?
Answer 430 people
Why 260 + 170 = 430.
Two Journeys: A train went 185 km, then 236 km. How far in total?
Answer 421 km
Why 185 + 236 = 421.