Ruth has a beaker containing a solution of 800 mL of acid and 200 mL of water. She thinks the solution is a little strong, so she drains 150 mL from the beaker, adds 150 mL of water, and stirs the solution. Ruth thinks the solution is still too strong, so again she drains 150 mL from the beaker, and adds 150 mL of water. How many mL of water are now in the beaker?
After draining 150 mL from the beaker, Ruth is left with 800 mL - 150 mL = <<800-150=650>>650 mL of acid.
After adding 150 mL of water to the beaker, the total volume of the solution becomes 650 mL + 150 mL = <<650+150=800>>800 mL.
After draining another 150 mL from the beaker, Ruth is left with 800 mL - 150 mL = <<800-150=650>>650 mL of solution.
After adding 150 mL of water to the beaker, the total volume of the solution becomes 650 mL + 150 mL = <<650+150=800>>800 mL.
Thus, there is 800 mL of water in the beaker now. Answer: \boxed{800}.
Let's break down the steps to find the final amount of water in the beaker:
1. Initial Solution: The beaker initially contains 800 mL of acid and 200 mL of water.
2. First Adjustment: Ruth drains 150 mL from the beaker and adds 150 mL of water.
- After draining 150 mL of acid, the remaining acid volume becomes 800 mL - 150 mL = 650 mL.
- After adding 150 mL of water, the water volume becomes 200 mL + 150 mL = 350 mL.
3. Second Adjustment: Ruth again drains 150 mL from the beaker and adds 150 mL of water.
- After draining 150 mL of acid, the remaining acid volume becomes 650 mL - 150 mL = 500 mL.
- After adding 150 mL of water, the water volume becomes 350 mL + 150 mL = 500 mL.
Therefore, the final volume of water in the beaker is 500 mL.