8) This is inverse variation because you can multiply both sides by 3 to get y = 6/x. In this case, it matches up with y = k/x and k = 6.
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10) This is not direct variation, nor inverse variation. We cannot write it in either y = kx or y = k/x form
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12) This is inverse variation. Rewrite 5/(2x) as (5/2)/x or 2.5/x; note how 5/2 = 2.5, so in this case k = 2.5
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14) This is direct variation. Multiply both sides by 4, and do a bit of rearranging and you should end up with y = (20/3)x, so we see it matches up with y = kx and k = 20/3.
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16) Cross multiply to get xy = 16, then divide both sides by x to end up with y = 16/x. This equation is in the form y = k/x with k = 16, so it is actually an inverse variation equation.