## anonymous 5 years ago Determine which, if any, of the three statements are equivalent. Give a reason for your conclusion. I) If the cat does not have claws, then the cat cannot scratch the furniture. II) If the cat can scratch the furniture, then the cat has claws. III) If the cat has claws, then the cat can scratch the furniture. a. I and II are equivalent b. I and III are equivalent c. II and III are equivalent d. I, II, and III are equivalent e. None are equivalent

1. saifoo.khan

this is hard.

2. anonymous

The first thing you need to do is transform these statements into statements using propositional logic: $p = \text{cat has claws}$$q = \text{cat can scratch furniture}$ 1) $$\neg p \implies \neg q$$ 2) $$q \implies p$$ 3) $$p \implies q$$ Since 1 & 2 are contrapositions of each other, therefore they are logically equivalent. However 3 is not equivalent to 1 or 2. Therefore I would say the answer is $$a$$

3. anonymous

To be more specific the converse of a statement is not logically equivalent to the statement.

4. anonymous

So to be clear p->q does not imply q->p

5. anonymous

Do you understand?

6. anonymous

heck no!!!

7. saifoo.khan

LOL.

8. anonymous

saifoo not funny!

9. anonymous

Here, I will explain. Lets look at these two statements: $p=\text{"it is raining"}$$q=\text{"i am getting wet"}$ Suppose $$p \implies q$$ If it is raining, then I am getting wet. Is that the same as $$q \implies p$$? If I am getting wet then it is raining. The answer is clearly no. Do you understand so far?

10. anonymous

You could be getting wet, even when it is not raining (shower for instance).

11. anonymous

saifoo not funny!

12. anonymous

okay i get that part!

13. anonymous

So we've established that $$p \implies q$$ does not necessarily mean $$q \implies p$$. However, as I have stated before. I have made the claim that if $$p \implies q$$ then $$\neg q \implies \neg p$$. So $$p \implies q$$ is If it is raining then I am getting wet. Is that the same as $$\neg q \implies \neg p$$ If I am not getting wet, then it is not raining. Well we have stated that if it is raining then I am getting wet. So if I am not getting wet then it is not raining, or the first implication would not hold. Do you see how these two are logically equivalent?

14. anonymous

yes i understand now!

15. anonymous

So now apply this to the original problem. Do you see how only the first two statements about the cat are logically equivalent?

16. anonymous

saifoo not funny!

17. anonymous

so what is my awser

18. anonymous

Well look at the choices. What do you think is the correct answer?

19. anonymous

A sound reasonable!

20. anonymous

Yes, A is the correct answer.

21. anonymous

so how wouldi right this!

22. anonymous

23. anonymous

Once you fully understand those two concepts, it will be immediately clear that only 1 & 2 are equivalent.

24. anonymous