Ideas for Teaching 2-Digit Addition

How Can I Teach My Child to Add 2-Digit Numbers?

Expand 2-Digit Numbers

If your child can already add single-digit numbers and understand place values, you can start on 2-digit addition by teaching him how to expand 2-digit numbers. This means that you would break down a number, such as 52, into the equation 52 = 50 + 2. You can demonstrate this concept with construction paper strips and blocks. Cut a sheet of construction paper into several strips, and write 10 on each one as the value. Each block has a value of one.

For this example, let's use the equation 52 + 46 = ? Your child would choose strips and blocks for each number. He can count out five strips and two blocks for 52; show him that this is 50 + 2. Then he can do the same for 46. Ask him to count all of the strips (nine) and blocks (eight) to write the answer for the equation, which is 98.

Use Branching

Once he understands this, add what is sometimes known as 'branching,' which involves expanding the numbers in the equation by drawing an upside-down V between each of them. Below the first upside-down V, write '50 + 2' on the left and '40 + 6' on the right. From these numbers, draw diagonal lines from the two tens numbers (50 and 40) to form a V, and have him write 90 below it. He'll do the same for the 2 and 6, writing 8. Add a + sign between the 90 and the 8. Another V is drawn from the 90 and the 8, and 98 is written below it.

Convert Equations to a Vertical Format

Equations That Don't Require Borrowing

Next, show your child how to write his equations in a 2-line format. To the side of this new format, write the first steps of his branching format plus the answer.

50 + 2
+ 40 + 6
-----------
90 + 8

Teach him to write the answer doing the ones column first and moving to the left. Once he gets used to doing this, you can show him how to solve vertical equations that require borrowing.

Equations That Do Require Borrowing

To demonstrate how to solve problems that require borrowing, begin by adding a single-digit number to a 2-digit number.

35
+7
---

Under the 7, write 12. Then emphasize that in the answer you can only put one digit in the ones column, and one digit in the tens column. Show him how to 'borrow' the 1 and put it at the top of the tens column. Then he can add the numbers in the tens column together. The answer to this problem is 42.

Once he has mastered this, give him problems for adding two 2-digit numbers. When the answer in the tens column is two digits, have him write the first digit over the invisible hundreds column and add that column.