Cogito
Grade 3 Math · Chapter 2 · Lesson 2
Rounding to the Nearest Hundred
The same rule, one place bigger.
10 problems · about 12 minutes · 3.NBT.A.1
What this lesson teaches
The child rounds a three-digit number to the nearest hundred.
- Find the two hundreds either side.
- Halfway is 50 past the lower one.
- Then decide which side the number is on.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Rounding to the Nearest Ten: Round 73 to the nearest ten.
Answer 70
Why 73 is before halfway, so it rounds to 70.
Review — Multiplication and Division Word Problems: 5 boxes with 8 pens each. How many pens?
Answer 40
Why 5 × 8 = 40.
Warm Up
Straightforward practice. Get the method working first.
4 problemsRound 649 to the nearest hundred.
Answer 600
Why 649 is just before halfway, so it rounds to 600.
When rounding to the nearest hundred, which digit decides?
Answer The tens digit.
Why The tens tell you which side of halfway you are on.
Round 271 to the nearest hundred.
Answer 300
Why Past 250.
Round 512 to the nearest hundred.
Answer 500
Why Before 550.
Build It Up
The same ideas with more to keep track of.
2 problemsRound 750 to the nearest hundred.
Answer 800
Why Exactly halfway rounds up.
Round 96 to the nearest hundred.
Answer 100
Why Between 0 and 100.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Stadium: 438 tickets were sold. Roughly how many, to the nearest hundred?
Answer 400 tickets
Why 438 is before halfway, so it rounds to 400.
The Big Nine: Round 309 to the nearest hundred.
Answer 300
Why 309 is nowhere near 350, so it rounds to 300.