Math Rules For Addition

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.

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.

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.

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.

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.

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.

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.