Explanation for Question 18 From the Math (No Calc) Section on the Official Sat Practice Test 8
So question number 18 gives us a system of equations and it's asking us, 2 which of the following is the value of Y. 3 So for looking for Y just a quick little trick, 4 is that what you want to do is solve one of the equations for 5 X. So that way, what you plug in actually has Y in the equation. 6 And so it'll probably be pretty easy to solve this bottom equation for X, 7 right? I can do that by subtracting three Y from both sides. 8 And I get the X is equal to 9.5 minus three Y, 9 and I can now take this expression and plug it in up here into 10 my top equation. So I get negative, 11 but instead of writing X, right, 9.5 minus three, 12 Y 9.5 minus three, 13 Y plus Y is equal to negative 3.5. 14 Now I have one variable. One equation is simple and I just solved, 15 right? 16 So I'll start by distributing the negative one. 17 That's in front of my parentheses and I get negative 9.5. 18 Now it's plus three Y plus three Y plus Y is equal to 19 negative 3.5. I think combine like terms with the three Y and the plus, 20 Y that'll give me four Y so it's still negative 9.5 21 plus four, Y is equal negative 3.5. 22 The next step to get Y on its own is to add 9.5 to 23 those sides. So I can get rid of the 9.5. 24 So that's going to be for why I'm doing 9.5 minus three w 3.5, 25 which will give me six. Right? So for Y is equal to six. 26 That means that I need to divide both sides by four to get Y 27 on its own. And so Y is equal to six over four, 28 but we want to simplify this fraction. I can divide the top and the 29 bottom by two. And so I get three over two as my answer. 30 So Y is equal to three over two.