You want 2 gallons of a 4% solution. How many ounces of the active herbicide are needed?

• A. 8 oz
• B. 10 oz
• C. 12 oz
• D. 14 oz

Answer: (B)

The task is to figure out how much active ingredient is needed to reach a specific concentration in a given final volume. For a 4% solution, 4 parts of the active herbicide are present per 100 parts of the final mixture, so the amount of active needed equals the final volume multiplied by 0.04.

First convert the final volume to the same unit used for measuring the active ingredient. Two gallons equals 2 × 128 = 256 fluid ounces. Multiply by 0.04: 256 × 0.04 = 10.24 ounces of active herbicide.

The closest practical measure in whole ounces is 10 ounces, which yields a concentration very near 4% (about 3.9%). Using 8 ounces would give a lower concentration, and 12 ounces would be higher, so 10 ounces is the best fit.