Explanation for Question 13 From the Math (Calc) Section on the 2020 October Sat
So number 13 is asking us in what year will we have more than 2 90 teachers? And so we can use our teacher equation, 3 which is 80 plus N and we're going to want to solve for N 4 right, which gives us years, 5 but we can ask ourselves what should T be equal to? 6 Because I want a number of teachers that is greater than 90. 7 So key T can't be equal to 90. 8 And I can't have half of a teacher or a quarter of a teacher, 9 right? It's one teacher or nothing. So if I need to be greater than 10 90, then that means I should have at least 91 teachers. 11 So rather than setting my equation equal to 90, 12 because 90 is no good. I want to be greater than 90. 13 I'll set it equal to 91. Then I'll say that's equal to 80 plus 14 N. And that also tracked 80 from both sides. 15 So I can get in and I get 11 is equal to N. 16 And so maybe you're tempted now to choose 2011, 17 right? Because you see the 11, but you have to remember the N is 18 the years since 2002. 19 And so 11 years after 2002 is actually 2013. 20 So the correct answer for question 13 is going to be B.