Explanation for Question 34 From the Math (Calc) Section on the Official Sat Practice Test 4
So here, we're looking at question number 34, 2 which says that in the study of migration habits, 3 240 mailbox may bats and 160 female bats 4 or tags. Right? So that means that they just put like a little chipper 5 or a bracelet on them so that they could keep track of the bats. 6 Then we need to know if 100 more female bats are tagged, 7 right? So we're adding a hundred more female bats. 8 How many male bats must be tagged. 9 So that three fifths of the total number are male. 10 All right. So first let's focus on this number, 11 right? Three out of five of the total. 12 So that's male over total. So we can use 13 this year first to figure out what the total number of bats is. 14 And then we'll use that proportion to solve for male. 15 So essentially step one here is figuring out how many total bats were tagged. 16 And we started with 240 male, and then we went on with 160 female, 17 but then we have a hundred more female, 18 right? So if I add those all together, at this point, 19 I have two 40 plus one 60 plus 100, 20 my total number of bats being 500. 21 But, and here's the tough part. We're actually doing more than 500 here, 22 right? Because I ended up tagging more male bats. 23 Right. But I don't know how many, so I start with 500, 24 I'm going to go tag more males so that I can get this ratio, 25 but we don't know how many more. So that's like having X males, 26 right. And unknown variable. So in reality, 27 my total is 500 plus X, 28 where X is the number of male bat...