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Solving Simple Proportions (page 4 of 5) Sections: Ratios, Proportions, Checking proportionality, Solving proportions Solving proportions is simply a matter of stating the ratios as fractions, setting the two fractions equal to each other, cross-multiplying, and solving the resulting equation. You'll probably start out by just solving proportions, like this:
2 : x = 3 : 9 First, I convert the colon-notation ratios to fractions: .2/x = 3/9 Then I solve: .2/x
= 3/9
(2x + 1) : 2 = (x + 2) : 5 First, I convert the colon-notation ratios to fractions: (2x + 1)/2 = (x + 2)/5 Then I solve: .(2x
+ 1)/2
= (x + 2)/5
Once you've solved a few proportions, you'll move into word problems, where you'll have to invent the proportion, extracting it from the word problem, before solving it.
.(inches)/(centimeters)
:
12/30.48 = 30/c
Thirty inches corresponds to 76.2 cm.
First, I need to convert the "two feet four inches" into feet: four inches is four-twelfths, or one-third, of a foot, so: 2 feet + 4 inches = 2 feet + 1/3 feet = 7/3 feet Then set up the proportion and solve: .(length)/(weight)
:
10/128 = ( 7/3
)/w
Since this is a word
problem, you may want to round to a practical number. The answer is:
.(value)/(tax)
:
7000/1100 = v/1400
Since this is a dollars-and-cents problem, I need to round the final answer to two decimal places: The assessed value is $8909.09. Copyright © Elizabeth Stapel 2006-2008 All Rights Reserved
I'll label the length of the short piece as "x". Then the long piece must have a length of 21 – x. (short piece) :
(long piece):
2 : 5 = x : (21 – x)
Then the length of the long piece is given by: 21 – x = 21 – 6 = 15 The pieces are 6 meters long and 15 meters long. << Previous Top | 1 | 2 | 3 | 4 | 5 | 6 | Return to Index Next >>
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