Explanation for Question 1 From the Math (No Calc) Section on the 2017 October Sat
Question one asks for the system of equations above what is the value of 2 X plus Y. So I'm going to start here by finding 3 what X is equal to. And I can do that by taking this bottom 4 equation and moving to I to the other side. 5 So X plus two, Y is equal to four. 6 And if you subtract two Y from both sides, 7 X is equal to negative two Y plus four. 8 Now that we know that we can plug that into our top equation up 9 here. So we know that two times negative two Y plus four, 10 I'm just plugging that in for X minus Y is equal to 11 eight. We can factor to get negative four Y plus 12 eight plus negative. Y is equal to eight. 13 We can add and subtract like terms negative five Y plus eight is equal 14 to eight. And if we subtract eight from both sides, 15 we get negative five. Y is equal to zero or Y is 16 equal to zero. Now we can plug that into one of these top equations. 17 I'm going to use the bottom one. So X plus two times zero. 18 So just zero is equal to four or X is equal to four. 19 So we know that X is equal to four. Y is equal to zero, 20 which means that X plus Y we're four plus zero is just equal to 21 four. And the correct answer is.
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