[Video] Q9: 3x + 4y = -23 2y -x = -19 what is the solution x y ( , ) to the system of equations above?

Explanation for Question 9 From the Math (No Calc) Section on the Official Sat Practice Test 1

So number nine gives us a systems of equations and our goal is to 2 solve for the system, right? And a test taking strategy here would 3 be to see that they want you to solve for two variables. 4 But if you can be smart and only solve for one, 5 that's going to be the best strategy because it will save you time. 6 Now, if you look at all the Y variables, you'll see that no matter 7 what you get, you won't, or most likely you won't be able to make 8 a final decision. Because if you get negative six, 9 you would still have to solve for X because you wouldn't be able to 10 S to decide between C and D. Now, 11 if you look at the X variables, you can see that each X is 12 different here. So the best strategy is going to be to solve for X, 13 because once you've solved for X, you'll be able to pick a final answer 14 choice and you don't actually have to solve for Y. 15 So let's go ahead and let's do elimination here, 16 and let's make sure to rewrite our second equation so that the X's and 17 the Y's lineup. And now if I want to solve for the X variable 18 or the X value, I want to cancel out the why's. 19 So I'm going to multiply this bottom equation by negative two. 20 That way I have a positive four and a negative four, 21 and my wise will cancel out. So I get two X minus four, 22 Y is equal to 19 times two, 23 so positive 38. And now this bottom equation, 24 as it was originally, we're no longer using it. 25 And we're going to use the modified version. That's multiplied by nega...