Decimal Operations

Adding Decimal Numbers When adding decimal numbers you must line up the decimal points in the numbers you are adding as well as in the answer. Whole numbers are on the left side of the decimal point and fractional numbers are on the right side.

Example Find the sum of 2+.07+3.2+.032 (Find the sum tells you to add) 2.000 remember you can add 0.070 zeros (in red)to even up the 3.200 numbers! + 0.032 5.302

Subtracting Decimal Numbers You must line up the decimal points in the numbers as well as in the answer. Whole numbers go on the left side of the decimal point and fractional numbers go on the right side of the decimal point.

Example Find the difference of 5.36 and .082. 5.360 Remember you have nothing 0.082 to subtract the two from if 5.278 you do not add a zero at the top!

Multiplying Decimal Numbers You need to line up the numbers as you normally would for multiplication without trying to line up the decimal points. In other words, disregard the decimal point until you get ready to put it in the answer. You will need to count the number of digits behind the decimal point in each number multiplied and move the decimal point in the answer that many places from the right of the answer.

Example Find the product of 3.2 and .056 Tip: Put the .056 on the top to multiply because it has more digits. .056 (3 digits behind the decimal) X 3.2 (1 digit behind the decimal) 112 1680 .1792 (move the decimal point over four places from the right in the answer)

Division of Decimal Numbers If you are dividing a decimal number by a whole number just bring the decimal point up to the top line and divide as usual. If you are dividing a decimal number by a decimal number, move the decimal point in the divisor to the right until it is a whole number. You must then move it that many places in the dividend (even if the dividend is a whole number) and bring it up to the line. Then you can just divide as usual.

Example Find the quotient of 84 and 2.40. You would set it up as 84 divided by 2.40. You would move the decimal point to the right two places in 2.40 to make it 240. You would then move the decimal point two places in 84 to make it 8400. Now you have 8400 divided by 240 and can divide as usual to get 35.