Decimals

• Decimals are a type of fractional number• The denominator is always a power of 10• A decimal point is used to show that it is less than 1

The decimal 0.5 represents the fraction 5/10

The decimal 0.25 represents the fraction 25/100

What decimal is represented by the fraction 461/1000? 0.461

Significant Digits or Figures• Significant digits are the most important parts

of the number

• They tell you how precise a number or measurement is

• They are the digits after the decimal point and after any zeros

• Trailing zeros count as significant digits

0.000567significant digits34

0

Positions• Positions tell us how much each digit is worth,

like they do for whole numbers• They are the number of spaces each digit

is behind the decimal point

0 . 0 0 0 0tenths

hundredths thousandths

ten thousandths

Addition

• Line up the decimal points to make sure everything is in the correct column

• Add like you would integers

0.587 + 0.036 = 0.5870.036+0.623

Subtraction

• Line up the decimal points to make sure everything is in the correct column

• Subtract like you would integers

0.587 - 0.036 = 0.5870.036-0.551

Multiplication

• Move the decimal point of the first number to the left one space for each position behind the decimal point of the second number

• Multiply that new number by the whole number value of the second number (ignore decimal point)

• Make sure to fill in any missing zeros

0.07 x 0.3 = x 3 = 0.021One position behind decimal

0 070

Division• Like multiplication, but move the decimal point of the

first number to the right one place for each position behind the decimal point of the second number

• Divide that new number by the whole number value of the second number (ignore decimal point)

0.08 ÷ 0.4 =One position behind decimal

÷ 4 = 0.2 0 80

Review• Decimals are fractional numbers where the

denominators are powers of 10

• Significant digits tell you how precise the number is

• Decimals add and subtract like integers

• Multiplying two decimals makes a smaller decimal

• Dividing two decimals makes a larger number