(Post updated: Nov 10, 2018)

Whoa! Since when can you use a ruler on the SAT? Well, you can’t use a traditional ruler, but you can use the edge of your paper like a ruler. Let me show you how it works.

What is the area of the square? Well, we can measure it using the side of the paper. Mark off the length of 4. We can see that each side of the square is a little less than 4. (We also know that the hypotenuse is the longest side of a right triangle – so we KNOW that each side is a little less than 4.)

So, if the sides were 4 (which we know is too long), the area would be 16. We know it must be less than this, so we can cross out answers C, D and E. We are in a great guessing position now. If we wanted to go further, eyeballing my ruler, it looks like the side is about 1/4 less than the length of 4. 1/4 of 4 is 1. So each side of the square is about 4-1, or 3. The area of a square with sides of 3 is 9. Choice A is the closest to this estimate.

Can you use this trick on this much harder problem? This is from Test 5, Section 4, Question 36. How can you figure out the size of angle A?