Four cups of a salad blend containing 40% spinach is mixed with an unknown amount of a salad blend containing 55% spinach. The resulting salad contains 50% spinach.How many cups of salad are in the resulting mixture?

Let x be the cups of the 55% spinach blend. The first 4 cups contain 4 × 0.40 = 1.6 cups of spinach. Set the spinach amounts equal: 1.6 + 0.55x = 0.50(4 + x), which gives x = 8. The total mixture is 4 + 8 = 12 cups, so the correct choice is 12.

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