DECIMAL OPERATIONS Decimal Cheat Sheet Adding and Subtracting decimals (courtesy of softschools.com) When asked to add or subtract decimals, the most important step is to line up the decimal points. The steps to adding and subtracting are this: 1.) Line up the place values of the numbers by lining up the decimals. 2.) Add in filler zeros if needed. 3.) Add or Subtract the numbers in the same place value positions. Adding: Ex.1) 13.6 + 17.8 Step 1: Line up the decimal points so that similar place values are lined up. (Remember, the tens place in both numbers should be lined up, the ones place in both numbers should be lined up, etc.) Step 2: Add the digits together that are lined up. Ex. 2) 14.86 + 22.9 If the numbers do not have the same number of digits after the decimal point, you can use "filler zeros" to help you line up the numbers. Subtracting: The steps for subtracting numbers with decimals are exactly the same as adding decimals. Let's take a look at a couple of examples. Ex. 3) 239.83  125.51 First we will line up the numbers by making sure the decimals are lined up. Then we just subtract the numbers that are in common place value positions. Ex. 4) 98.3  45.67 We will start by lining them up. In the subtraction examples, the filler zeros are even more helpful. Some make the mistake of placing a 7 in the hundredths place of the answer. However, take a look at what happens with the filler zero. With the zero here, we can see that we need to borrow in order to subtract. Multiplying Decimals Step 1: Multiply the numbers and ignore the decimal points. Step 2: Count up how many number of digits that come after the decimal points in both factors. Step 3: Place the decimal in the product so that the same number of digits comes after the decimal point in the answer. Step 4: (Optional) Estimate the answer to see if your answer and the placement of your decimal point are reasonable.
