Column addition
You learn to add big numbers by writing them in columns and adding one column at a time.
How to work it out
- Line up in columns: ones under ones.
- Start on the right.
- If a column sum is 10 or more, write the ones and carry 1 ten to the next column.
11
347
+265
612
A worked example
347 + 265
- Ones: 7 + 5 = 12, write 2 and carry 1.
- Tens: 4 + 6 + 1 = 11, write 1 and carry 1.
- Hundreds: 3 + 2 + 1 = 6.
- The answer is 612.
More examples
486 + 379
- Ones: 6 + 9 = 15, write 5 and carry 1.
- Tens: 8 + 7 + 1 = 16, write 6 and carry 1.
- Hundreds: 4 + 3 + 1 = 8.
- The answer is 865.
11
486
+379
865
654 + 178
- Ones: 4 + 8 = 12, write 2 and carry 1.
- Tens: 5 + 7 + 1 = 13, write 3 and carry 1.
- Hundreds: 6 + 1 + 1 = 8.
- The answer is 832.
11
654
+178
832
Watch out
You forget the 1 you carried: for 347 + 265 you write 502.
Write the carried 1 small in the next column straight away, and add it in there.
You line the numbers up on the left instead of on the right.
Ones must be exactly under ones. So line the numbers up on the right.
Tips
- Write the carried digit small in the next column.
- Estimate first: 347 + 265 is about 350 + 250, so about 600.
Exceptions
- If one number has fewer digits, like 47 + 265, still line it up on the right and leave the empty places blank.
Why it works
When ones are under ones and tens are under tens, you only ever add two small numbers. You start on the right, because a column that makes 10 or more carries 1 to the column on its left. That way you do not miss anything.