Consecutive integers: Average of a Set = Average of First and Last Terms

$$M$$ is the set of all odd integers between $$A$$ and $$B$$. If $$A$$ and $$B$$ are even integers such that $$A \lt B$$, what is the average (arithmetic mean) of $$M$$?

Correct. [[snippet]] When you plug in $$A=2$$ and $$B=8$$ into this answer choice, you get >$$\frac{A+B}{2} = \frac{2+8}{2} = \frac{10}{2} = 5$$ This is the right answer choice because all other answer choices are eliminated for the same Plug-Ins.

Incorrect. [[snippet]]

$$\frac{A-B}{2}$$

$$\frac{A-B}{2}+1$$

$$\frac{A+B-1}{2}$$

$$\frac{A+B}{2}$$

$$\frac{A+B+1}{2}$$