Answer Choices
−20
−8
−4
8
Explanation for Question 6 From the Math (No Calc) Section on the Official Sat Practice Test 3
So looking at number six, we can see that we have a systems of 2 equations problem, and we can also immediately notice that rather than asking us for 3 just X or just Y the question actually asks us for an expression X 4 minus Y. And I can tell you from experience looking at through these problems, 5 that whenever the sat asks you for an expression, 6 what you'd really want to do here is try to solve for that expression 7 directly. Um, it is possible to go through the whole process, 8 solve for X, then solve for Y then plug them in. 9 But it's going to be a lot faster actually to use an elimination method 10 so that you can come up with this expression in one step, 11 really. And I'll show you how we can do that here. 12 First I'll copy things down, right. 13 And I'll think about for this particular problem, 14 adding them straight down. Right. Because I know that I want a coefficient of 15 one on X and I want a coefficient of negative one on Y. 16 Right? And so if I add straight down, 17 right, so that things don't cancel out, I actually get five X minus five. 18 Y is equal to negative 20. I noticed that I come up with something 19 really close to X minus Y it just has the fives in the way. 20 So what I can do here is factor out of five. 21 So that it's right in this five X minus Y is equal to negative 22 20. And now I have what I'm looking for the X minus Y it's 23 just multiplied by five. So my next step would be to divide both sides 24 by five. That way the five that's in my way, 25 cancels out I'm left with X minus Y is equal to negative four, 26 which is why our best answer here is going to be C. 27 Right? So again, I want to reiterate, you don't have to do this particular 28 process, which takes a little bit of intuition of how to maneuver the equation 29 around you can solve for X and then solve for Y, 30 but it will be faster to use the elimination method here.