Once an electrical system has been installed and is considered to be an existing system, no safety-related design concepts can be implemented to eliminate or mitigate electrical hazards.
true / false.

False.

Explanation:

We can implement the safety related designs or devices to eliminate or mitigate after the installation of electrical system. For example we can install fuses in our homes or offices which detect if the current in the circuit exceeds it's limit. After the one fault fuse has to replaced with other one. There are many other electrical safety equipment that can be installed later on after the system installation.

the total distance that martina travels that day is

(distance from home to mom's office) plus (distance from mom's office to school)

plus (distance from school to library) plus (distance from library to friend's house)

plus (distance from friend's house to martina's house).

(we don't know what any of these distance actually is.)