A pharmacist has 80 milliliters of a 25 percent saline solution. Which expression can be used to find the percentage concentration of the final solution if she adds x milliliters of a 10 percent saline solution?

The original solution contains 0.25 × 80 milliliters of salt, and the added solution contributes 0.10 × x milliliters. The final volume is 80 + x milliliters, so the concentration as a percentage is (0.25 × 80 + 0.10 × x) ÷ (80 + x) × 100. This is choice B.

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