Final answer:
The calculation shows that to dilute a 15% alcohol solution to a 10% solution by adding water, 10 ounces of water is needed, but this option is not available in the provided choices, which may indicate an error in the question.
Step-by-step explanation:
The student wishes to dilute a 15% alcohol solution to a 10% solution. To solve this, we need to know the amount of pure alcohol in the original solution first, which is 15% of 20 ounces. This can be calculated as 0.15 × 20 ounces = 3 ounces of alcohol. The amount of alcohol remains the same after dilution, but the total volume of the solution changes. If we let x be the number of ounces of water to be added to achieve a 10% alcohol solution, the new total volume would be 20 ounces + x. The equation representing the dilution is (3 ounces) / (20 ounces + x) = 10% or 0.10.
Now, solving for x, we get:
3 / (20 + x) = 0.10
3 = 0.10 × (20 + x)
3 = 2 + 0.10x
3 - 2 = 0.10x
1 = 0.10x
x = 10 ounces.
However, none of the provided answer options suggests adding 10 ounces. Therefore, there may be an error in the question as the only logical answer based on the calculations made is 10 ounces of water, which is not listed in the options. The student may need to recheck the question or the answer options provided.