Explanation for Question 4 From the Math (Calc) Section on the 2019 October Sat
Now a number four, we're told that the function F as defined above, 2 um, for, for that function, what is the value of F of 20? 3 And so when we see F of 20, 4 right, we can think about F of X and we see that 20 is 5 where the X used to be. So essentially all we need to do here 6 is take the 20 and plug it in to the function above, 7 right? So I'll write alphabet X is equal to X plus 0.25 8 X, times 50 minus X. 9 And now to find F of 20 wherever I see an X I'll just 10 plug in a 20. So it becomes 20 plus 0.2, 11 five times 20 times 50 minus 20 is, 12 and now we can do the math right 0.2, five times 20, 13 that's going to be five or 20 divided by four, 14 right? And that's 20 plus five times 50 minus 20 that's 15 30. So what we really have here is a 25 times 16 30. We know that 25 times three is 75. 17 So 25 times 30 must be 750. 18 And so our best answer is going to be C.