Concept 8 of 8
Rounding: The Nearest Neighbour
Today's big idea
Find the halfway mark: 5 or more rounds up, less than 5 rounds down.
Rounding snaps a number to the nearer round neighbour on the line.
How it works
👀 What's going on?
Is 47 closer to 40 or to 50? Rounding answers that in one glance, by snapping a number to the nearest round number instead of carrying it around exactly.
💡 Here's the trick
Look at the number line above. Every number sits between two round neighbours, and there is a halfway mark exactly between them. If the number is past halfway it snaps up to the higher neighbour, and if it is before halfway it snaps down to the lower one.
🪄 How to do it
- 1.Find the two round numbers your number sits between, and mark the halfway point.
- 2.Look at the deciding digit: for the nearest 10 it is the ones, for the nearest 100 it is the tens.
- 3.If that digit is 5 or more, round up. If it is less than 5, round down.
✍️ Try it
Round 47 to the nearest 10. Then round 462 to the nearest 100.
For 47, the ones digit is 7, which is 5 or more, so it rounds up to 50. For 462, the tens digit is 6, which is 5 or more, so it rounds up to 500.
⚠️ Watch out
You might be thinking a number that feels close to a round hundred always rounds to it. Check the deciding digit, not your gut. 448 rounds to 400, not 500, because the tens digit 4 is less than 5, even though 448 feels near 500.
🌟 Why this matters
Rounding is how you estimate quickly, check whether an answer is sensible, and read prices and crowds at a glance. Next year it grows to rounding big numbers to the nearest thousand and beyond, so the halfway rule you learn here does all the heavy lifting later.
Exam tip: Underline the deciding digit first; every rounding question turns on that one digit.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Round 473 to the nearest 100.”
- 1
Find the neighbours
473 sits between 400 and 500, halfway at 450. 🎯
- 2
Look at the deciding digit
Nearest 100 is decided by the tens digit: 473 → 7.
- 3
Apply the rule
7 is 5 or more, so round up.
- 4
Answer ✓
473 rounds to 500
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Round 47 to the nearest 10. Which round number is it closer to?
Quick check
✅ VERIFICATION
Round 68 to the nearest 10.
⚡ Finish the activity above first to answer.
Keep going!