What is the diameter of the tank used in the chlorine mass calculation?

• A. 30 ft
• B. 22 ft
• C. 25 ft
• D. 27 ft

Answer: (D)

Knowing how much chlorine to add starts with the tank’s volume. For a cylindrical storage tank, the volume depends on the radius (which comes from the diameter) and the length. The radius is half the diameter, so changing the diameter changes the cross‑sectional area and thus the overall volume dramatically, especially if the ends are curved or the tank is long. Once you have the volume, you convert to gallons and multiply by the desired chlorine concentration to get the mass needed. In this problem, a diameter of 27 ft gives the volume that matches the chlorine mass specified; using any other diameter would produce a different volume and, therefore, a different required mass.