Rounding to 10 and 100

Sometimes we don't need an exact number — we just need a quick, easy-to-remember answer. About 50, about 300. That's what rounding is for.

What "rounding" means

When you round a number, you swap it for the nearest round number — a number that ends in 0 (or 00, or 000…). Round numbers are easier to talk about and easier to add in your head.

47 ≈ 50 (nearest ten)

312 ≈ 300 (nearest hundred)

Round to the nearest 10

To round to the nearest 10, look at the ones digit:

• If the ones digit is 0, 1, 2, 3 or 4 — round down (drop it).
• If the ones digit is 5, 6, 7, 8 or 9 — round up (add to the tens).

Examples:

Round to the nearest 100

To round to the nearest 100, look at the tens digit:

• If the tens digit is 0, 1, 2, 3 or 4 — round down (the hundreds stay, tens and ones become 0).
• If the tens digit is 5, 6, 7, 8 or 9 — round up (add one to the hundreds).

Examples:

The number-line picture

Imagine the number sitting on a line between two round numbers. Whichever round number is closer wins.

184 is closer to 200 than to 100.

312 is closer to 300 than to 400.

When the number is exactly halfway (the tens digit is 5 and the rest is 0), the rule says round up. So 650 rounds to 700, not 600.

Why we round

• Quick mental math: 198 + 401 ≈ 200 + 400 = 600. Pretty close to the real answer (599).
• Estimating costs: a sandwich for $4.79is"about$5".
• Talking about big numbers: "the school has about 300 children" is easier to remember than "297".

Try it

• 🎯 Round to 10 and 100 — practice both
• 📏 Number line to 1,000 — see how close numbers really are

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