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A PROPORTION is a pair
of equal ratios
Proportions
can include different units of measurement
(ie: hours, feet, pounds, etc.)
~~~
The units MUST be
the SAME
across the TOP and BOTTOM
or
along the LEFT and RIGHT
sides.
~~~
If the units of measure ONLY match diagonally,
then the ratios will not form a
proportion.
~~~
Cross Products
are found by
multiplying the
Top value in the first ratio X Bottom value in
the second ratio
and
Bottom value in the first ratio X Top value in
the second ratio
To form a Proportion
the Cross Products MUST be Equal
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Example 1:
3 ft./10 min. = 6
ft./20min.
The units are the SAME
across the TOP & BOTTOM,
The cross multiplying is
3 x 20 = 60
10 x 6 = 60
The cross products are equal
So this example
WOULD BE a Proportion.
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Example 2:
8 ft./10 ft. = 16
sec./20 sec.
The units are the SAME
along
the LEFT & RIGHT
sides,
The cross multiplying is
8 x 20 = 160
10 x 16 = 160
The cross products are equal
So this example
WOULD BE a Proportion.
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Example 3:
5 ft./9 min. = 18
in./19 min.
The units are NOT the SAME
along the TOP & BOTTOM sides,
or across the LEFT & RIGHT
So this example
WOULD NOT BE a
Proportion.
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Upon further review:
4/6
and 2/3
4x3 = 12
and 6x2 = 12
This
is a Proportion
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5/8 and 3/9
5x9 = 45
and 8x3 = 24
This
is NOT a Proportion
Let's Practice
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