[Video] Q29: The incomplete table above summarizes the number of left-handed students and right-handed students by gender for the eighth-grade students at keisel middle school. there are 5 times as many right-handed female students as there are left-handed female students, and there are 9 times as many right-handed male students as there are left-handed male students. if there is a total of 18 left-handed students and 122 right-handed students in the school, which of the following is closest to the probability that a right-handed student selected at random is female? (note: assume that none of the eighth-grade students are both right-handed and left-handed.)

Explanation for Question 29 From the Math (Calc) Section on the Official Sat Practice Test 3

So right now we're looking at question number 29, 2 which gives us a pretty blank table, 3 um, right here. And then it's asking us to find the probability that our 4 right-handed student selected at random is female. 5 Um, and so in order to find that probability, 6 we need to know, right. The, 7 um, the number of right-handed females. 8 And in order to do that, we're going to use this information from earlier 9 in the, um, in the question where it says, 10 um, that there are five times as many right-handed female students as a left-handed 11 female students. So we'll call left-handed female students. 12 A and if there are five times as many right-handed than we know that 13 the right would be five times a, and then if we're looking at nine 14 times as many right-handed male students, as left-handed male students, 15 we'll call this B. Um, and so we know that this right will have 16 to be nine times B because they're not, there's nine times as many. 17 And now we can actually use this information here to create a systems of 18 equations, right. We know that a plus B is equal to 18, 19 right? That would be all of our left-handed people. 20 Um, and then we also know that five times a plus nine times B 21 is equal to 122. That's going to be all of our right-handed people. 22 And so we can do is we can take this topic equation, 23 maybe subtract B from both sides. And we now get the a is equal 24 to 18 minus B. And so we can take this information and plug it 25 into our equation ...