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questioner

Post subject: GRE Geometry (Numerical Entry) Posted: Fri Sep 23, 2011 11:51 am 

Joined: Sun May 30, 2010 3:15 am Posts: 424

A scale drawing of a rectangular garden plot measures 5 inches by 7 inches. If the longer side of the garden plot is 21 feet, what is the area, in square feet, of the actual garden plot?
The correct answer is 315.
You can solve this quickly by setting up a ratio: 5/7 = x/21. Cross multiplying yields 105 = 7x, so x = 15, which is the width. Now find the area = length × width, and you get area = (21)(15) = 315 square feet.  The length of the garden is expressed in feet. Thus the lenght of the area in inches is 21 × 12 = 252. The proportion becomes: 5/7 = x/252, and the value of x so found is 180. The area of the actual garden plot is: 180 × 252 = 45360 squared inches which in feet is 3780.


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mathematician

Post subject: Re: t.4 s.4 qt.13: geometry, proportions Posted: Fri Sep 23, 2011 12:04 pm 

Joined: Fri Sep 23, 2011 12:02 pm Posts: 1


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questioner

Post subject: Re: t.4 s.4 qt.13: geometry, proportions Posted: Wed May 02, 2012 4:15 am 

Joined: Sun May 30, 2010 3:15 am Posts: 424

Don't you need to convert inches to feet before creating the proportions? I converted 5 in. to .41 ft, 7 in. to .58 ft, then created the proportion to cross multiply and solve for x, which came to 14.8 – my area was 311.7 and wrong. Why so? Isn't mine more accurate?


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Gennadiy

Post subject: Re: t.4 s.4 qt.13: geometry, proportions Posted: Wed May 02, 2012 4:16 am 

Joined: Sun May 30, 2010 2:23 am Posts: 498


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