A proportion
is a comparison of ratios.
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A proportion
is an equation that states
that two ratios are equal, such as
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Proportions
always have an EQUAL sign! |
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A
proportion can be written in two ways:
Both
are read "4 is to 8 as 1 is to 2".
In
each proportion the first and last term (4 and 2) are
called the
extremes.
The second and third terms (8 and 1) are called the
means. |
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In simple
proportions, all you need to do is examine the
fractions. If the fractions both reduce to the same value,
the proportion is true. |
This is a true
proportion, since both fractions reduce to 1/3. |
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In simple
proportions, you can use this same
approach when solving for a missing part of a proportion.
Remember that both fractions must reduce to the same
value. |
To alter the
denominator 3 to become 15 requires multiplying by 5. The
SAME must be done to the top to keep the fractions equal.
Answer: x = (1)(5) = 5 |
This
simple approach may not be sufficient when working with more complex
proportions.
You need a rule:
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Some
people call this rule
Cross
Multiply!! |
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Rule:
In a true proportion, the
product of the means equals
the product of the extremes. |
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Example:
Solve for x in this
proportion:
Solution:
Apply
the rule that the product of the means
equals the product of the extremes.
5x = (25)(2)
5x = 50
x=10 Answer
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