SAT Intensive Drill – Luyện Tập Nâng Cao Chuyên Sâu

Correct Answer: 5

Explanation: To solve this problem, denote the amount of the 20\% salt solution the chemist needs to mix with the pure water as x liters. Starting with pure water (0\% salt) and aiming for a 10\% salt solution, the total volume of the final mixture will be 5+x liters. The salt content from the 20\% solution is 0.20xliters (20\% of x), and the salt in the final solution should be 10\% of the total volume, or 0.10(5+x) liters. Setting up the equation 0.20x=0.10(5+x) allows us to solve for x. The chemist needs to mix 5 liters of the 20\% salt solution with 5 liters of pure water to achieve the desired 10\% salt concentration in a total volume of 10 liters.