Pre Algebra (Period 2 & 4)

Adding & Subtracting Decimals Equations 3-5

Most important... LINE UP THE DECIMALS!!
We did a number of examples from the textbook... check out this section!!


Make sure you use a SIDE BAR for your calculations!!


Multiplying & Dividing Decimal Equations 3-6


For multiplication, count the decimals and place the decimal from the right!!
THese are difficult to show here as well...but

( m/7.2) = -12.5

multiply both sides by -7.2

(-7.2)(m/-7.2) = -12.5(-7.2)
m = 90

Make sure to use a side bar and multiply carefully!!

s/2.5 = 5

multiply both sides by 2.5

(2.5)(s/2.5) = 5(2.5)
3 = 12.5


4.5 = m/-3.3

multiply both sides by -3.3
Notice your answer will be a negative!!

(-3.3) (4.5) = [m/-3.3](-3.3)

-14.85 = m

... and I used a sidebar in class to show the multiplication!!

For division

0.9r = -5.4
Divide both sides by 0.9

.9r = -5.4
0.9 0.9

r = -6

use a sidebar to divide carefully

divide both sides by -0.9
-0.9n = -81.81

-0.9n/-0.9 = -81.81/-0.9

notice that your solution will be a positive!!
and use a side bar to divide carefully

n = + 90.9