Can someone explain this math question to me?

Test Preparation SAT Preparation
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<p><a href="http://i584.photobucket.com/albums/ss284/sear_squid/SAT/ScreenShot2014-03-30at203041_zps108595be.jpg"&gt;http://i584.photobucket.com/albums/ss284/sear_squid/SAT/ScreenShot2014-03-30at203041_zps108595be.jpg&lt;/a&gt;&lt;/p>

<p>Basically, I answered the question correctly by picking clever values for a, b, and c.</p>

<p>For a: 21
For b: 7
For c: 1</p>

<p>I feel like I got lucky on this question. They give you an explanation, but I'm still not sure how THEY arrived at the answer. Can someone, please, clarify? Thanks in advance.</p>

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<p>type in photobucket where the stars are, followed by a dot com.</p>

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<p>If you can’t get to it, it’s March 29th’s SAT Question of The Day.</p>

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<p>I came here to answer your question but you didn’t post it.</p>

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<p>If a, b, and c are numbers such that a/b=3 and b/c=7, then (a+b)/(b+c) is equal to which of the following?</p>

<p>A: 7/2 (The correct answer)
B: 7/8
C: 3/7
D: 1/7
E: 21</p>

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<p>If a/b=3 then that means that a/b is equal to 3/1 thus a is 3 and b is 1. Same for c/d. C/d equals 4/1 thus c=4 and d=1. (3+4)/(1+1) is equal to 7/2.</p>

<p>Do you get it now?</p>

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<p>Yes, I do. Thanks!</p>

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<p>^Hawk - where does D come in?</p>

<p>How about, if a/b=3 then that means that a/b is equal to 3/1 thus a is 3 and b is 1 OR a is 21 and b is 7. Same for b/c. If b/c = 7, and b = 7 then c=1 and b+c=8. Then, (a+b) / (b+c) = (21+7) / (7+1) = 28/8 = 7/2.</p>