A tank is 74.5 ft in diameter and 42.5 ft to the overflow. If there are 1,375,000 gal of water in the tank, what is the psi at the bottom of the tank?

• A. 12.5 psi
• B. 25.0 psi
• C. 18.3 psi
• D. 9.8 psi

Answer: (C)

The pressure at the bottom depends only on how tall the water column is above that point, not on the tank’s diameter. Water depth is 42.5 ft, and 1 ft of water head equals about 0.433 psi, so the bottom pressure is 42.5 × 0.433 ≈ 18.4 psi.

Using 62.4 lb/ft^3 for water density gives the same result: (62.4 × 42.5) / 144 ≈ 18.4 psi. The provided volume helps check consistency with the tank size, but the pressure calculation relies on depth alone.

Therefore, the pressure at the bottom is about 18.3–18.4 psi, with 18.3 psi being the closest option.