Question

half the sum of x and y decreased by one-third y

Answer 1

$$
\large{
\cfrac{1}{2}\left(x+y\right)-\cfrac{1}{3}y\\
=\cfrac{1}{2}x+\left (\cfrac{1}{2}-\cfrac{1}{3}\right )y\\
=\cfrac{1}{2}x+\cfrac{1}{6}y
}
$$
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