SAT Math questions encourage “silly errors”. Unfortunately, the computer that will score your test won’t care in the slightest that you were “on the right track” or “got the idea”—it will only detect that you were just wrong.
That’s why you should do a “sanity check” on your answer choice by estimating that answer BEFORE you attempt to solve the problem. This is especially important when the answer choices are all real numbers.
An example: “What is x if 4(pi)/x = 12?”
First, estimate the answer—subsitute ‘3’ for ‘pi’ (it’s close enough). Then (4×3/x) = 12; or 12/x = 12.
So x has got to be “AROUND 1”.
Now, if you hose something up in the calculations, you’ll at least KNOW IT! If you don’t get an answer close to “one”, you know you’ve made an error and need to go back and try again.
Another example: If you’re looking for an angle within a triangle, it can’t POSSIBLY be more than 180 degrees, right?
Whenever you can easily put in mind a “ballpark figure” for your answer, DO IT, and make sure your chosen answer is somewhere in that neighborhood.
SAT Prep Plan: SAT Tips 
