[Video] Q12: If 2a/b =1/2, what is the value of b/a ?

Explanation for Question 12 From the Math (No Calc) Section on the Official Sat Practice Test 8

So question 12 gives us this equation here. 2 Two a over B is equal to one half, and they want us to 3 solve for B over a. And so there's two things we could do here. 4 We have two strategies. One strategy is to solve for an equation that looks 5 exactly like this B over a, or we could solve for B on its 6 own and then a on his own, and then divide them either way. 7 You should get the same answer, but perhaps one of the faster ways is 8 going to be to solve for this whole fraction together rather than trying to 9 do a separate. So that's what we'll try to do here. 10 We have two, a over B is equal to one half. 11 And so the first thing I can do is cross multiply. Cause that's going 12 to get rid of my fractions, which I like to do for now because 13 our fraction is the opposite of how we want it. Right? 14 So if I cross multiply, I do two times two a, 15 which is going to give me foray as a foray. 16 And I do B times one, which will give me B. So I now 17 have four a is equal to B and I'm looking for B over a, 18 so if I want B over a, then I need to divide both sides 19 by a right. These A's will cancel and I get four is equal to 20 B over a, and so our correct answer is going to be deep.