Not impressed by the practical exercise. It has a relatively complex concept that has not been introduced (Opening an application) and I believe the walkthrough instructions are incomplete:
An alternative way is to enter the full path of the executable file into the FileName parameter of the Open Application activity, as shown below. The full path in this instance would be C:\Windows\System32\notepad.exe…
…says nothing about specifying the selector that is a mandatory requirement.
Much more appropriate at this point in the training would be a much simpler WriteTextFile activity (and an Assign resultString to (“correct” or “incorrect”)) after the FlowDecision, which would be much more in keeping with the level of this exercise, imho.