Cogito
Grade 3 Math · Chapter 2 · Lesson 1
Rounding to the Nearest Ten
Which ten is it closer to?
10 problems · about 13 minutes · 3.NBT.A.1
What this lesson teaches
The child rounds a two- or three-digit number to the nearest ten using a number line.
- Every number sits between two tens.
- Find halfway, then see which side the number is on.
- Exactly halfway rounds up.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
2 problemsReview — Multiplication and Division Word Problems: 5 boxes with 8 pens each. How many pens?
Answer 40
Why 5 × 8 = 40.
Review — Multiplying by 0 and 1: 7 × 0 = ?
Answer 0
Why Seven lots of nothing is nothing.
Warm Up
Straightforward practice. Get the method working first.
4 problemsRound 73 to the nearest ten.
Answer 70
Why 73 is before halfway, so it rounds to 70.
What happens to a number that is exactly halfway?
Answer It rounds up.
Why Exactly halfway always rounds up.
Round 34 to the nearest ten.
Answer 30
Why Before halfway.
Round 68 to the nearest ten.
Answer 70
Why Past halfway.
Build It Up
The same ideas with more to keep track of.
2 problemsRound 25 to the nearest ten.
Answer 30
Why Exactly halfway rounds up.
Round 291 to the nearest ten.
Answer 290
Why Between 290 and 300.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsThe Crowd: 62 people came to a show. Roughly how many is that, to the nearest ten?
Answer 60 people
Why 62 is before halfway, so it rounds to 60.
Exactly Halfway: Round 85 to the nearest ten.
Answer 90
Why Exactly halfway rounds up, so 85 becomes 90.