How to add two-digit numbers (for example 40 + 50).

• Place one number above the other so the tens' place digits and ones' place digits are lined up. Draw a line under the bottom number.

40
50

• Add the two ones' place digits. (0 + 0 = 0). Place the zero below the line in the ones' place column.

40
50
 0

• Add the numbers in the tens' place column (4 + 5 = 9) and place the answer below the line and to the left of the ones' place sum

40
50
90