It's fun to be good at math, and it's nice to understand how the underlying algebra on a tough word problem works. But if you're aiming for top scores, it's imperative that you cast a critical eye on your own ability to tease the "math way" of solving a problem out of the problem during the fairly tight time constraints imposed by the SAT.
If x + y = p and x – y = q, what is p2 + q2 in terms of x and y?Like all questions, there's a "math way" to do this, but unlike all questions, this one is a prime candidate for plugging in. There will be some students who can breeze through the algebra in their head and identify the correct answer almost instantly. If that's you, then great. You needn't plug in. But if that's not you, or if you only kinda think that's you, then you should probably just plug in. It's fast, it'll get you the right answer, and then, later on you can go home, make an awesome couch fort, and figure out the algebra when you're not pressed for time.
(A) 2(x + y)2
(C) 2x2 – 2y2
(D) 2(x2 + y2)
(E) 2(x2 – 4xy + y2)
The plugging in solutionSay x = 3 and y = 2. Then 3 + 2 = p = 5, and 3 - 2 = q = 1. 52 + 12 = 26, so you're looking for an answer choice to give you 26. Type the answer choices into your calculator carefully, substituting 3 for x and 2 for y, and you'll be done in a hot second:
(A) 2(x + y)2 = 2(3 + 2)2 = 50
(B) 4xy = 4(3)(2) = 24
(C) 2x2 – 2y2 = 2(3)2 – 2(2)2 = 10
(D) 2(x2 + y2) = 2(32 + 22) = 26
(E) 2(x2 – 4xy + y2) = 2(32 – 4(2)(3) + 22) = –22
Now add 'em up:
Not impossible, right? Totally doable. But arguably more involved than the plug-in solution above.
The bottom lineLook, I really just want you to be happy. If you want the algebra, I'll give you the algebra. But I really think it's a good idea for you to know how to plug in, too. Because if you have to ask me for the algebra on a question like this, that means it wasn't obvious to you right away when you encountered it on the test. And that means there's a good chance that when you sit down for the real thing, the algebra isn't going to be obvious to you for every single question. And if, when the algebra isn't obvious, you don't have a backup plan, then you're doing yourself a disservice.
Try the algebra first, if that's your bent. But you should have a few other tricks up your sleeve for the questions where the "math way" isn't jumping off the page onto your lap.