Addingsubtracting

1
Adding/subtracting Multiplying/dividing
Decimals

• Sections 5.2 5.3

2
Adding/Subtracting Decimals

• To add decimals, line up the decimal points,
  insert zero(s) to the right of the last digit to
  make the number of places the same, and add the
  columns of digits as usual.
• EXAMPLE
• 15.52 2.371

3

• To subtract decimals, follow the procedure for
  adding and use the borrowing procedure if
  necessary.
• EXAMPLE
• 5.8 3.92

4
MORE EXAMPLES

• 34.567 129.43 2.8903
• 53 29.31

5
Working with Negative Decimals

• To add/subtract with negative decimals, follow
  the same procedure as when working with
  addition/subtraction of integers. So, ALWAYS
  change the subtract to add and change the sign
  that follows.
• EXAMPLES
• 8.1 (-99.2) -3.4 9.6

6
MORE EXAMPLES

• -1.05 (-7.23)
• Subtract 18 from -26.99

7
Evaluation Solution Testing w/ Decimals

• To evaluate, substitute the values for the
  variables and perform the indicated operation.
• To solution test, substitute the value for the
  variable and see if the left side of the equation
  equals the right.

8
EXAMPLES

• Evaluate y z for y 11.6 and z 10.8
• Is 12.1 a solution of the equation y 4.3 7.8
  ?

9
Simplifying by Combining Like Terms

• Recall that like terms are terms with the same
  variable(s) to the same power(s).
• EXAMPLE
• Simplify by combining like terms
• -4.3x 7.8 - 20.1x 14.6

10
Multiplying/Dividing Decimals

• To multiply decimals you DONT have to line up
  the decimal points. Multiply as usual and then
  find the total number of places to the right of
  each factor. This number is used to determine the
  placement of the decimal point in the answer. To
  get that place, start at right end of your answer
  and count over that number of places putting the
  decimal point where you end up.

11
Examples

• 45.9 x .42 .0721 x 48 (5.4)(-1.3)

12
Multiplying by Powers of 10 (e.g. 10, 100, 1000,
10,000 etc.)

• Move the decimal point to the right the same
  number of decimal places as there are zeros in
  the power of 10.
• Examples 203.004 x 10 1.15 X 1000
• (-.092 x -10,000)

13
Circumference of a Circle

• The circumference (i.e. perimeter) of a circle is
  found by the formula
• Circumference pi radius
• Example Find the circumference of a circle
  whose radius is 5 inches. Use 3.14 for pi.

14
Word Problem

• A woman is fertilizing her garden. She uses 5.6
  ounces of fertilizer per square yard. The garden
  measures 60.5 square yards. How much fertilizer
  does she need?

15
Dividing Decimals
Quotient

Dividend
Divisor

• Steps to Divide
• 1. Move the dec. pt. in the divisor to the
  right until you get a whole number.
• 2. Move the dec. pt. in the dividend to the
  right the same of places.
• Divide. Put the dec. pt. in the quotient
  directly over the moved dec. pt. in the
• dividend.

16
EXAMPLES