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Solving Proportions: More Examples (page 6 of 7) Sections: Ratios, Proportions, Checking proportionality, Solving proportions Another category of proportion problem is that of "similar figures". "Similar" is a geometric term, referring to geometric shapes that are the same, except that one is larger than the other. Think of what happens when you use the "enlarge" or "reduce" setting on a copier, or when you get an eightbyten enlargement of a picture you really like, and you'll have the right idea. If you've used a graphics program, think "aspect ratio".
Now I'll find the length of c. Copyright © Elizabeth Stapel 20012011 All Rights Reserved
c
× 48 = 21 × 68 For my answer,
I could just slap down the two numbers I've found, but those numbers
won't make much sense without their units. Also, in rechecking the
original exercise, I notice that I'm supposed to round my values to
the nearest whole number, so "29.75",
with or without units, would be wrong. The right answer is: b = 35 mm and c = 30 mm.
In other words, the photo lab will be maintaining the aspect ratio; the rectangles representing the outer edges of the pictures will be similar figures. So I set up my proportion and solve: 9 × 3.5 =
5 × h The picture will be 6.3 inches high. In the first exercise above, the ratios were between corresponding sides, and the proportionality was formed from those pairs of sides; for instance, (length of lefthand slanty side on big triangle) : (length of lefthand slanty side on little triangle) = (length of base on big triangle) : (length of base on little triangle. In the second exercise above, the ratios were between the two different dimensions, and the proportionality was formed from the sets of dimensions: (original height) : (original length) = (enlarged height) : (enlarged length). For many exercises, you will be able to set up your ratios and proportions in any of various ways. Just make sure that you label things well, clearly define your variables, and set things up in a sensible and consistent manner; this should help you dependably reach the correct solutions. If you're ever not sure of your solution, remember to plug it back into the original exercise, and verify that it works. << Previous Top  1  2  3  4  5  6  7  Return to Index Next >>



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