Someone please help me! 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 Jess. Use an indirect proof to show that Shelly did not leave the key in the security office door.

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

Question

Someone please help me! 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 Jess. Use an indirect proof to show that Shelly did not leave the key in the security office door.
 
Hint: Begin by assuming Shelly did leave the key in the door.

anonymous · Answer

May someone please help me on this question?

radar · Answer

this calls for a logical mind, and that leaves me out.  Sorry.

anonymous · Answer

If the manager is correct, if we can assume that, then what Jess says is correct.
Shelly did not do that.

The formalism is beyond me.
And a bit silly, to tell the truth.

anonymous · Answer

We don't need a proof by contadiction to show that.

anonymous · Answer

ok. thanks for trying!