Explanation for Question 18 From the Math (Calc) Section on the 2019 April Sat
So for number 18, we are looking at this two way table here in 2 order to calculate probability. And the hardest thing about these kinds of questions 3 is knowing exactly which rows and columns you are looking at. 4 And for that, you just have to pay close attention to what the word 5 problem is saying. So let's start looking at it. 6 Sarah recorded the gender and eye color of all the students in her biology 7 class. The results are shown in the table above if a male student is 8 selected at random from Sierra's biology class, 9 what is the probability that he will have brown eyes? 10 So first let's remember our equation for probability. 11 It is desired over total. 12 So basically what you're looking for over the total of everything. 13 So first I think it would be easier to find our total, 14 which is what we are selecting from. 15 We are not selecting from females and males. 16 So we cannot look at this total. 17 We are only selecting from male students. 18 So that means mirror looking at this column, 19 and this will be the total that we use. 20 So that will be our denominator. 21 So now we are looking for the probability that he will have brown eyes. 22 Now let's look at this row for the brown eyes. 23 We need the number of males that have brown eyes as our top, 24 since that is our desired. And we can see that that is six. 25 So the probability that you'll have brown eyes is six over 15, 26 but that is not in simplest form. We can divide the top and bottom 27 by three. So that is a probability of two over five, 28 which is B.