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# Plugging In: Basic Technique

What must be added to $$\frac{b+a}{2}$$ to obtain $$\frac{a-b}{2}$$?
Correct. [[snippet]] For the values of $$a=5$$ and $$b=3$$, this answer choice matches your **goal value** of -3. All other answer choices are eliminated by the same plug-in, so this is the right answer choice.
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]]
Incorrect. [[snippet]]
$$-b$$
$$-a$$
$$2b$$
$$2a$$
$$b-a$$