(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

"Watson, I have uncovered the following facts:

* If Mrs Smith is lying then Moriarty has not escaped

* Either Moriarty is dead or he is really Jones

*If Moriarty is really Jones then he has escaped.

*I am convinced Mrs Smith is lying.

"Good Lord Holmes," replied Dr Watson, "what can you make of all this?"

"Elementary my dear Watson, Moriarty is dead."

Is Holmes correct? Justify your answer.

2. Relevant equations

3. The attempt at a solution

So I started by

Let

A = Mrs. Smith is lying.

B = Moriarty has escaped.

C = Moriarty is really Jones.

D = Moriarty is dead.

so then we have

A→~B

D→~C

C→B

A

_______

∴ D

Is this the correct way of setting out the Argument.... I was a little confused as how to approach theeitherin the second line.

And the last line before the conclusion should that just be A?

After this am I supposed to use a contradiction to prove it??

ie do I assume that D is false??

This is really confusing me!

Help Please..

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Valid and Invalid Arguments

**Physics Forums | Science Articles, Homework Help, Discussion**