Copyright Goodheart-Willcox Co., Inc. May not be reproduced or posted to a publicly accessible website. 8 Section 1 Whole Numbers Carrying Only one digit can occupy a single column. What happens when the sum of num- bers in a single column reaches or exceeds 10 and has a value that occupies two columns? In the following example, adding the numbers in the units column results in 15. The 5 is placed under the units column and the 1 is carried to the next column. Moving the second digit of a sum up a column in value is called carrying. Whenever a single column’s sum totals a value of 10 or more, move the higher valued numbers one column to the left. 1 1 2 2 2 1 2 1 9,966 21 991 256 + 94,531 105,765 When you carry a number, write the carried number at the top of the next column and make it smaller than your other digits. Next, add the tens column. The result is 26. Write in the number 6, and carry the 2 to the hundreds column. Continue in this manner until all columns are added. Always check your accuracy. Look for Tens When adding a column, search for combinations of numbers that add up to 10. In the single-column example shown, 8 plus 2 equals 10, and 1 plus 9 equals 10 (those add up to 20, so far), and 4 plus 6 equals 10 (totaling 30). The remaining digit is 7, so the total is 37. You will fi nd it easier doing the mental calculations this way. Be sure to write tick marks next to the numbers as you add them or you may forget which ones you have already added: 9 7 2 ✓ 6 4 1 + 8 ✓ 37 Checking Addition by Adding Up and Down Always check your math work. If you added by going up the column, then check it by adding going down.