Question

PLEASE HELP!!!!!!

Answer 1

Shelly, Jess, and Andrea are all working at an amusement park for the summer. The manager finds out that one of them left the key in the door to the security office. When he asked them who did it, they replied:

Shelly: Andrea did it.
Jess: Shelly did not do it.
Andrea: I didn’t do it.

The manager believed Andrea. Use an indirect proof to show that Andrea did not leave the key in the security office door.

Hint: Begin by assuming Andrea did leave the key in the door.

Answer 2

Look now, this requires simple logical calculus of negations, conjunctions and disjunctions.
it is highly UNadvisable to apptoach all this by "common sense" approach - not because it is impossibel, but because it is cumbersome and lengthy.

Get ur hands on a simple logical calculus tutorial - they are a billion