A small day tank of sodium hypochlorite solution is 3.5 ft in diameter and loses 0.35 ft in 24 hours. How many milliliters per minute of hypochlorite solution was used?

• A. 66.17 mL/min
• B. 66 mL/min
• C. 66.2 mL/min
• D. 70 mL/min

Answer: (B)

When a cylindrical tank loses liquid height, the volume change equals the cross-sectional area times the change in height. The radius is half the diameter, so r = 1.75 ft. The cross-sectional area is πr^2 ≈ π(1.75)^2 ≈ 9.62 ft^2. A drop of 0.35 ft over 24 hours yields a daily volume loss of about 9.62 × 0.35 ≈ 3.37 ft^3. Converting to liters, 3.37 ft^3 × 28.3168 L/ft^3 ≈ 95.3 L per day (95,300 mL/day). Split over 1,440 minutes in a day, that's 95,300 / 1,440 ≈ 66.2 mL/min. Rounding to the nearest milliliter gives about 66 mL/min.