Solved: Math Pros Needed: Official SAT Study Guide, Incomplete Answer Key?

Test Preparation
1

<p>Okay, awkwardly, by rereading my own post, I have found my mistake. This thread can therefore be ignored, deleted or closed.</p>

<p>(Hi CC,</p>

<p>while studying for the math portion of the SAT using the Blue Book I have encountered a certain problem which has caused some troubles for me, or, more accurately, of which the provided solution in the answer key has seemed incomplete to me.</p>

<p>The problem I am talking about concerns Practice Test 6, Section 4, Problem 14.</p>

<p>There it is asked: "If 4(x+y)(x-y) = 40 and x - y = 20, what is the value of x + y?</p>

<p>What the CollegeBoard wants to see: We know that x - y = 20, thus we substitute 20 into the first equation. We end up with 20*4(x+y) = 40 and then solve for (x+y) = 1/2. The answer key accepts 1/2 or 0.5. </p>

<p>What I did (correctly in my opinion): By substituting and creating a matrix I ended up with
x = 10.25 and y = -9.75. The way I got there is fairly complicated, however, by substituting these values for the variables into both equations given in the problem, the equations works (,don´t they?). </p>

<p>That´s the reason for my confusion. Am I doing something wrong or not considering something I should consider?
If no, does it happen often that the answer keys are incomplete?</p>

<p>Thank you very much for the clarification.)</p>

2

<p>I’m not gonna bother to check if they work or not, you can do that yourself. Just so you know, you will never EVER have the time to do that on the actual test, so just do it the way everybody else and college board does it: (4)(20)(x+y)=40;(x+y)=1/2. The answer key is never incomplete, it will show you the easiest solution (in college board’s opinion) on how to do the problem. If you find an easier/quicker way to do the problem, then by all means go for it, but if not, just stick to the basics and you’ll get it right. SAT Math portion does not require precalc, let alone matrices.</p>