Cogito
Grade 3 Math · Chapter 2 · Lesson 4
Adding Within 1,000 Fluently
Faster now, with the blocks in your head.
10 problems · about 13 minutes · 3.NBT.A.2
What this lesson teaches
The child adds three-digit numbers within 1,000 fluently, composing tens and hundreds.
- Add hundreds to hundreds, tens to tens, ones to ones.
- Make a new ten or hundred when a column fills.
- Estimate first so you know what to expect.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
3 problemsReview — Estimating Sums and Differences: Estimate 406 + 195 to the nearest hundred.
Answer 600
Why 400 + 200 = 600.
Review — Rounding to the Nearest Hundred: Round 649 to the nearest hundred.
Answer 600
Why 649 is just before halfway, so it rounds to 600.
Review — Rounding to the Nearest Ten: Round 73 to the nearest ten.
Answer 70
Why 73 is before halfway, so it rounds to 70.
Warm Up
Straightforward practice. Get the method working first.
3 problems385 + 247 = ?
Answer 632
Why 385 + 247 = 632.
What should you do before adding big numbers?
Answer Estimate, so you know what to expect.
Why An estimate gives you something to check against.
347 + 285 = ?
Answer 632
Why 7 and 5 makes a new ten.
Build It Up
The same ideas with more to keep track of.
1 problem506 + 279 = ?
Answer 785
Why No tens in the first number.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
3 problems158 + 264 = ?
Answer 422
Why A new ten and a new hundred.
The Book Sale: 346 books were sold on Saturday and 285 on Sunday. How many in all?
Answer 631 books
Why 346 + 285 = 631.
Two Journeys: A trip of 429 km, then 268 km. How far in total?
Answer 697 km
Why 429 + 268 = 697.