7.2. Proportion Properties http://www.ck12.org
a)^45 = 30 x
b)y+ 81 = 205
c)^65 =^2 xx−+ 24
To solve a proportion, you need tocross-multiply.
a)
b)
c)
Example B
Your parents have an architect’s drawing of their home. On the paper, the house’s dimensions are 36 in by 30 in. If
the shorter length of your parents’ house is actually 50 feet, what is the longer length?
Set up a proportion. If the shorter length is 50 feet, then it will line up with 30 in. It does not matter which numbers
you put in the numerators of the fractions, as long as they line up correctly.
30
36
=
50
x−→ 1800 = 30 x
60 =xSo, the dimension of your parents’ house is 50 ft by 60 ft.
Example C
Suppose we have the proportion^25 =^1435. Write down the other three true proportions that follow from this one.
First of all, we know this is a true proportion because you would multiply^25 by^77 to get^1435. Using the three corollaries,
we would get: