Class Notes Adding And Subtracting Decimals

Class Notes Target Skill: Adding and Subtracting Decimals to the ten-thousandths place "to the ten-thousandths place" means there will be up to 4 digits past the decimal point in a number 1 . ones .

_ _ _ _ tenths hundredths thousandths ten-thousandths

First, the MOST important rule when adding and subtracting decimals is to keep the decimal points lined up (aligned).

+

. . . .

and

-

. . .

This rule does NOT work when multiplying decimals. When multiplying decimals DO NOT line up the decimal point. If the decimal point does line up when multiplying, it's just a fluke-not a rule. This rule does NOT work when dividing decimals. Dividing decimals has its very own rule. Second, once the numbers are lined up according to their decimal points there may be empty spaces. Fill in all empty spaces with zeros. This is called "annexing zeros". Third, add or subtract the decimals. When you arrive at the decimal point, bring the decimal point straight down to the answer position keeping it perfectly in line with all of the other decimals. NEVER, EVER add or subtract decimals across. ALWAYS add and subtract decimals up and down.

Hint: Neatness counts. If you are not neat, turn your ruled paper to the landscape view so the ruled lines go up and down instead of across and use the lines to force your numbers into straight columns. Thanks Ms. Diamond, for this tip. Graph paper can work well too.