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3-Digit Addition

Practise adding three-digit numbers, carrying across the ones, tens and hundreds columns.

Grade 3 · 3.NBT⚡ Place-value fluency
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How to add three-digit numbers

Three-digit addition uses the exact same method as two-digit — there is just one more column. A carry can now happen twice (ones into tens, tens into hundreds), so staying organised matters more.

  1. Add the ones; carry into the tens if it reaches 10.
  2. Add the tens plus any carry; carry into the hundreds if needed.
  3. Add the hundreds plus any carry.
  4. Write the full result.

Worked examples

Two carries256 + 178 — ones: 6 + 8 = 14 (write 4, carry 1); tens: 5 + 7 + 1 = 13 (write 3, carry 1); hundreds: 2 + 1 + 1 = 4. Answer: 434.
One carry341 + 215 — ones: 1 + 5 = 6; tens: 4 + 1 = 5; hundreds: 3 + 2 = 5. Answer: 556.
AD AREA (parent reading zone only — never shown during practice)

Tips & common mistakes

Keep the three columns straight and work strictly right to left. The chain of carries is where errors creep in, so an estimate is your safety net: 256 + 178 ≈ 260 + 180 = 440, close to 434.

  • Dropping a carry partway across — especially the tens-into-hundreds carry.
  • Columns drifting out of alignment with bigger numbers.
  • Adding left to right and missing later carries.

Frequently asked questions

What grade is 3-digit addition?

It is a grade 3 skill, extending the 2-digit method by one column.

How is it different from 2-digit addition?

Only in length — same method, one extra column, and the chance of carrying twice.

What if a carry happens twice?

That is normal. Carry from ones to tens, then if the tens also reach 10, carry again into the hundreds.

How can we check it?

Round each number and estimate the total, then compare to the answer.

My child aligns numbers wrong — any tips?

Graph paper or a column drawn on lined paper keeps ones, tens and hundreds in their own lanes.

Keep practising

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