Please explain question #8, section #4, SAT test #3! Thanks Mike!

The equation you’re given is y = 0.56x + 27.2, where y is the average number of students per classroom and x is the number of years since 2000. You’re asked what the number 0.56 represents in the equation.

Before you get too lost in the details of the particular model, recognize that y = 0.56x + 27.2 is really just a line in y = mx + b form! So without even thinking about average students per classroom or years, we know that 0.56 represents the line’s slope, or rate of change. Which answer choices refer to rates of change?

Really, only choice C does. A talks about a total number, B talks about an average number, and D talks about a difference (which is just one number minus another). Only C talks about an INCREASE, which is the kind of word we’re looking for to describe slope. So the answer must be C.