Math Rules for Addition

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General rules apply to addition when adding in columns, finding the sum of fractions, combining decimal numbers or in the use of negatives. You will want to know addition rules to build confidence and accuracy.

Adding In Columns

When adding multiple digit numbers in columns, all the "ones" are in the right column, the "10s" to the left, then the "hundreds" and so forth. Addition starts in the "ones" column, and if the sum is more then one digit, leave the last digit at the bottom of the column and carry the first digit(s) to the top of the next column.

Adding Decimals

To add decimals, the decimal points must be lined up vertically before you add the columns. Remember that each whole number can be written with a decimal to the right followed by a zero, such as 42.0 or 7.0.

Adding Fractions

To add fractions, the denominators must be the same. Use the lowest common multiple of each of the denominators, but whenever you multiply a denominator by a number, you must multiply the numerator by the same number.

Adding Like Terms

When adding terms, the variable(s) must be the same and they must be to the same power. For example: 2XY + 5 X + 4XY = 5X + 6XY.

Adding Negatives

When adding negatives, add as you would for positives, but your answer will be negative. Adding negatives does not change the sign; you simply have more of them.

Adding Positives And Negatives

To add a positive and a negative, subtract the two numbers, then give the answer the same sign as the number with the larger absolute value. If you have more negative than positive, your answer will be negative, and likewise, if there is more positive than negative, your answer will be positive.


About the Author

Leslye Hull is a mathematics instructor with a bachelor's degree in mathematics and also a master's degree in general ministries. Hull has been writing children’s stories and travel experiences since 1975. More recently, Hull has written several articles related to math for Demand Studios.

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