Numbers & Counting | Arithmetic | Fractions & Decimals | Prealgebra | Site Map

Adding Three-Digit Numbers

The numbers are getting bigger. Now that you have one-digit and two-digit addition under control, you need to move up and start working with values in the hundreds column (triple-digit numbers). Remember the process and work from right to left. Instead of stopping at the tens column, you'll just have one more column to work with. Let's look at some examples with no carrying.

456 + 123 = 579
281 + 715 = 996
809 + 150 = 959

And in a vertical format...

462 + 516 978

Looking at Carrying Again

Those examples gave you answers less than one thousand (1,000). It should be obvious that many of the three-digit numbers you add will give you a sum that is larger than 1,000. How do you get there? Bring back those carrying/regrouping skills.

When your column totals are greater than "9" you will need to carry the "1" into the next column to the left. A sum from the ones column that is greater than "9" will carry a "1" to the tens column. If you get a sum greater than "9" in the tens column, you will bring the "1" to the hundreds column. From the hundreds, you will move to the thousands. It's the same process that happens with two-digit numbers. If you feel like it's too much, just remember that you are only adding single digit numbers. We don't ask you to add all the numbers at one time. Break up the problem into a few simple steps. Math has rules to make things very straightforward.

Example:
573 + 769 = ?
Steps to Solve:
• Ones column: 3 + 9 =12
• Write the "2" and carry the "1".
• Tens column: 1 (carried) + 7 + 6 = 14
• Write the "4" and carry the "1".
• Hundreds column: 1 (carried) + 5 + 7 = 13
• Write the "13" and your final answer is "1342".
Answer:
573 + 769 = 1,342

Break it down into steps...

573 + 769 ?

1   573 + 769 2

11   573 + 769 42

573 + 769 1342

More Than Three Digits

Now that you know the basics of moving from one column to the next, you should be able to add any two values together. You will always use the same process: start with the column on the far right (ones column), and move towards the left. When you reach numbers called decimals, the rules will stay the same. But with decimals, you need to line up the decimal points before you start.

You can easily do these problems with the skills you have.

1,234 + 4,231 = 5,465

20,567 + 35,411 = 55,978

And in a vertical format:

65,872 + 2,781 68,653

Break it down into steps...

65,872 + 2,781 3

1     65,872 + 2,781 53

1 1     65,872 + 2,781 653

1 1     65,872 + 2,781 68,653

Remember, it's only one column at a time. After some practice this will be much easier.

Related Links