Explanation for Question 33 From the Math (Calc) Section on the 2019 April Sat
Uh, number three, it gives us a system of equations with solution X, 2 Y, and we want to know the value of X plus Y. 3 So first we can find the solution to the system. 4 I think the easiest way to solve the system would be using elimination. 5 So if we multiply this top one by negative two, 6 then the six X will cancel out with a negative six X. 7 So writing out the entire top equation, 8 we get negative six X minus four, 9 Y equals negative 32, 10 and then I will rewrite the bottom one below. 11 And now if we add them together, negative six X plus six X 12 it's just zero. So we can cross that out then negative four Y plus 13 two, Y is negative two Y and negative 32 plus 28 14 is negative four. 15 Now we can divide both sides by two and get that. 16 Y is equal to two. 17 Now we can take this value of Y and plug it into either equation 18 that we originally had. I'm going to plug it into the first one. 19 So three X plus two, 20 Y we found was two is equal to 16. 21 So three X plus four equals 16. 22 If we subtract four from both sides that leaves three X equals 23 12, then dividing by three X is equal 24 to four. So now we have X equals four and Y equals 25 two. So X plus Y is going to equal four plus two, 26 which is six.