Water distribution piping is to be hydrostatically tested. Take these criteria as given for this project: the test pressure must be at least 1.5 times the system's working pressure and in no case less than 100 pounds per square inch. The system's working pressure is 78 pounds per square inch. What is the minimum acceptable test pressure?

Where to look it up

Explicit exercise assumptions; not a universal code requirement.

Why C is correct

For this project, calculate 1.5 × 78 = 117 psi and compare it with the 100 psi floor. Both conditions must be met, so the minimum is 117 psi. A 78 psi or 100 psi test would fall short of the stated project requirement; 156 psi comes from an unspecified multiplier of 2. The calculation alone does not establish that 156 psi would damage equipment. Verify component ratings and the applicable test procedure, medium and duration before testing; the given project factors are not a universal plumbing-code rule.