Today’s SAT math question is about this number line:

and these three assertions:

I. AB + CD = AD

II. AB + BC = AD – CD

III. AC – AB = AD – CD

Which of these statements must be true?

I. AB + CD doesn’t equal AD, because BC is missing.

II. AB + BC is everything except for CD. Therefore, it does equal AD – CD.  This one is true.

III. AC – AB = BC. AD – CD = AC, not bc. Sorry, III, you are not true.

Work carefully on reasoning questions like this one and remember to look for the right answer! Some of these questions will ask you which answer is true, while others will ask you to find answers that cannot be true.