Who can help me with this old QOTD?

Test Preparation SAT Preparation
1

<p><a href="http://img.skitch.com/20090107-jm9ew66sr9kudbajhsp3mmufbw.jpg%5B/url%5D"&gt;http://img.skitch.com/20090107-jm9ew66sr9kudbajhsp3mmufbw.jpg&lt;/a&gt;&lt;/p>

<p>Thanks a lot. Even when I clicked the wrong answer, and got the "here's why," i still could't understand it! thanks again</p>

2

<p>a:b = 3 .Assume that a = 21 and b = 7 ==>21:7 =3
b:c = 7. You have assumed that b = 7 ==> c = 1
a+b/b+c = 21+7/7+1 = 28/8 = 7/2</p>

<p>Thats it.Simple solution in less than 30 seconds.THere is a more complicated one but this is enough.</p>

3

<p>hehe. I really like this problem.
a/b = 3 => a = 3b
b/c = 7 => b = 7c
Then a = 3.7c = 21c
(a+b)/(b+c) = (21c+7c)/(7c+c)= 28c/8c= 7/2
And that’s all.</p>