[Video] Q1: 2x - y = 8x + 2y = 4for the system of equations above, what is the value of x + y?

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

Question one asks us for the system of equations above what is the value 2 of X plus Y. So we to solve 3 this first need to find the value of X and the value of Y. 4 And this can be done using either elimination or substitution. 5 I'm going to use substitution, which means it'll solve for X in the second 6 equation, and then plug that X into the first. 7 So we've got X plus two, Y is equal to four slamming 8 through, we got X is equal to subtract two Y from each side, 9 we've got X is equal to four minus two Y. 10 Now let's plug that into the first equation. 11 So we have two X minus Y is equal to eight. 12 And then we know that X is equal to four minus two Y. 13 So we have two times four minus two Y minus Y 14 is equal to eight. Now sobbing through, 15 we've got eight minus two times two, 16 Y is four Y minus Y is equal to eight. 17 So solving through, we can subtract eight from each side and we 18 get negative five, Y is equal to zero. 19 So that means that Y is just equal to zero. 20 Now we also need to find the value of X because we were looking 21 for X plus Y and we have just plugged this. 22 Y is equal to zero into either expression. 23 I'm just going to choose the first one, pretty arbitrarily. 24 So we've got two X minus Y is equal to eight. 25 And then we know that Y is equal to zero. So we have two 26 X minus zero is equal to eight. 27 So two X equals eight X is equal to four. 28 So we're looking for the value of X plus Y that's 29 what the question is asking. It's asking, 30 what is the value of X plus Y and X plus Y is equal 31 to four plus zero. 32 So it's equal to four. We're going to pick B as our answer choice.