Explanation for Question 30 From the Math (Calc) Section on the 2018 May Sat
Question 30 asks if this relationship is modeled by the function, 2 M of D is equal to eight times 10 to the BD, 3 which of the following could be the values of a and B. 4 So the first thing I'm going to do is I'm going to sell for 5 a, using this part in the table where D is equal to zero. 6 So to do that, I'm going to plug in 120 on left side, 7 set that equal to a times 10 to the BD. 8 And it doesn't matter what B is here, cause D is equal to zero 9 and B times D then equals zero. 10 And this becomes 120 is equal to N or to a times 11 10 to the zero, which is just one. So 120 is equal 12 to, and from that we can eliminate answer choices, 13 a and B, which say that a is equal to 12. 14 So now we can knowing what AA is, 15 again, plug in the coordinates into this equation to solve for B. 16 So this time I'm going to use this second row here, 17 a hundred, 3.2, one is equal to 120 18 times 10 to the 30 B. 19 So I'm going to start by dividing both sides by 120. 20 And that gives me 0.8, 21 six is equal to 10 to the 30 B. 22 And what I noticed here is that 0.86 is a fraction. 23 So we need to somehow figure out which exponent is going to make 10 24 into a fraction. And that's going to be a negative exponent because negative exponent 25 just turn their base into a fraction. So we know that B is going 26 to have to equal a negative number for 30 B to equal a negative 27 number, which means that the only possible answer choice is D because C has 28 a positive value for B. So the answer is.