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7. DECIMALS, RATIO, PROPORTION, AND PERCENT
Definition.
A proportion is a statement that 2 ratios are equal.
Example.
Write a fraction in simplest form that is equivalent to the ratio 39 : 91.
39 13 · 3 3
39 : 91 =
=
=
91 13 · 7 7
Example.
Are the ratios 7 : 12 and 36 : 60 equal?.
Extremes: 7 · 60 = 420
The ratios are not equal.
Means: 12 · 36 = 432
Example.
B 2 14
Solve for the unknown in the proportion = .
8
18
⇣ 1⌘
1
18B = 8·2 =) 18B = 8 2+
=) 18B = 16+2 =) 18B = 18 =) B = 1
4
4
Example.
3x 12 x
Solve for the unknown in the proportion
=
.
4
6
18x = 4(12
x) =) 18x = 48
4x =) 22x = 48 =) x =
Example.
Solve the follwing proportions mentally:
1) 26 miles for 6 hours is equal to
for 24 hours.
104
48 24
=
22 11