SAT math question from the 2007-08 official practice test

<p>So here is the question. Its difficult to write out on a computer but I did my best. If you can't understand let me know. Maybe I can do something different. </p>

<ol>
<li>If x+y/a-b=2/3, then 9x+9y/10a-10b=</li>
</ol>

<p>(A) 9/10
(B) 20/23
(C) 20/27
(D) 2/3
(E) 3/5</p>

<p>Any help would be greatly appreciated :)</p>

<p>I got (E).</p>

<p>Since it is a proportion, x+y=2. So you can substitute this.
9x + 9y is factored as 9(x +y).
So 9(2) = 18
The numerator is done.</p>

<p>You can do the same for a-b=3. Substitute this.
10a-10b is the same thing as 10 (a-b)
So 10 (3) = 30</p>

<p>18/30 is simplified to 3/5 :D Hope this helps!</p>

<p>You can always just plug in numbers.</p>

<p>Say,
x = 1
y = 1
a = 5
b = 2</p>

<p>(1+1)/(5-2) = 2/3</p>

<p>So 9x+9y / 10a - 10b = (9+9)/(50-20) = 18/30 = 9/15 = 3/5</p>