Question

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.


My conclusion was this, can anyone tell me if my answer works? :

Assuming shelly didn't do it, then shelly

Answer 1

Aghh it didn't come out right, here is my answer to the question: Assuming shelly didn't do it, then shelly's statement that andrea did it is FALSE because we're assuming shelly did it. Jess's statement that shelly didn't do it is also FALSE because we're again assuming that shelly did do it. Andrea's statement that she didn't do it is TRUE because it was shelly who supposedly did it. Since two out of three statements are false, we can conclude that the opposite is true, Shelly did leave the key in the door.

Answer 2

I really can't follow, at the moment. I didn't do well in math proofs. But I think in your answer's first sentence you may have meant "Assuming Shelly DID do it,...". Not sure! Just take a look. Sorry! I'm a little braindead! I think you made a great effort! Unfortunately I don't think I'm smart enough to evaluate it!

Answer 3

Oops lol typo :( but thanks anyways