Addition of 3-Digit Numbers

After the number \(99\), the counting numeral is \(100\). That’s a \(3\)-digit number. Whenever one gets added with \(99\), the answer is \(100\).

Three-digit numbers begin at \(100\) and then proceed to \(999\). Then, you get into the thousands (or four-digit numbers). The addition of two \(3\)-digit numbers takes several steps.

Related Topics

• Adding 2-Digit Numbers
• Addition of Hundreds
• Addition of Four-Digit Numbers
• How to Add and Subtract Integers? 

How are three-digit numbers added?

Step one: Put one number over the other number so the hundreds, tens, and ones spots all line up. Place a plus sign \((+)\) to the left of these numbers. As an alternative to the equal sign \((=)\), place a line under the lower figure.

Note: Whenever addition expressions are stacked, be certain these numbers end up lined up properly. These numbers ought to always get lined up on the right. It doesn’t matter the quantity of these numbers you are adding; the ones on the right always get lined up.

Step two: Add digits in the ones’ spot. If that numeral is higher than \(10\), put a one above the tens spot column and put the ones’ under the line in the ones’ spot column.

Step three: Add the digits in the tens spot and put this answer under the line and in the tens spot column.

Step four: Add the numerals in the hundreds spot column and put this answer under the line and before the other numeral under that line.

As you see, problems involving stacks always get solved from right to left. That means you must always begin by adding the digits that are on the right.

Addition of 3-Digit Numbers – Example 1:

Find the sum.

\(\begin{array}{r} &352\\ +\!\!\!\!\!&135\\ \hline \end{array} \)

Solution:

First line up the numbers: \(\begin{array}{r} &352\\ +\!\!\!\!\!&135\\ \hline \end{array}→ \) Add the numerals in the ones’ spot column \((2 + 5 = 7)\) and put the resulting answer under the line. \(\begin{array}{r} &352\\ +\!\!\!\!\!\!&135 \\ \hline \end{array} \\ \ \ \ \ \ \ \ \ \ \ \ 7\), Continue with tens’ place. \(5 \ + \ 3=8\), \(\begin{array}{r} &352\\ +\!\!\!\!\!\!&135 \\ \hline \end{array} \\ \ \ \ \ \ \ \ \ 8\). Add the numerals in the hundreds’ spot column, then put this answer under the line. \(3 \ + \ 1=4\), \(\begin{array}{r} &352\\ +\!\!\!\!\!\!&135 \\ \hline \end{array} \\ \ \ \ \ \ \ 487\)

Addition of 3-Digit Numbers – Example 2:

Find the sum.

\(\begin{array}{r} &273\\ +\!\!\!\!\!&432\\ \hline \end{array} \)

Solution:

First line up the numbers: \(\begin{array}{r} &273\\ +\!\!\!\!\!&432\\ \hline \end{array}→ \) Add the numerals in the ones’ spot column \((3 + 2 = 5)\) and put the resulting answer under the line. \(\begin{array}{r} &273\\ +\!\!\!\!\!\!&432 \\ \hline \end{array} \\ \ \ \ \ \ \ \ \ \ \ \ 5\), Continue with tens’ place. \(7 \ + \ 3=10\). The numeral is \(10\). Put a one above the tens spot column and put the \(0\) under the line in the one’s spot column. \(\begin{array}{r} &273\\ +\!\!\!\!\!\!&432 \\ \hline \end{array} \\ \ \ \ \ \ \ \ \ 0\). Add the numerals in the hundreds’ spot column, then put this answer under the line. Whilst adding the numbers in the hundreds column, you also add the tens number which you carried forward from your one’s \(2 + 4+1=7\), \(\begin{array}{r} &273\\ +\!\!\!\!\!\!&432 \\ \hline \end{array} \\ \ \ \ \ \ \ 705\)

Exercises for Addition of 3-Digit Numbers

1. \(\color{blue}{750+224}\)
2. \(\color{blue}{820+170}\)
3. \(\color{blue}{445+352}\)
4. \(\color{blue}{634+315}\)

1. \(\color{blue}{974}\)
2. \(\color{blue}{990}\)
3. \(\color{blue}{797}\)
4. \(\color{blue}{949}\)