Law School Discussion

Another Game -- Exam 33, sec 4, #11 (forest)

nemo

Another Game -- Exam 33, sec 4, #11 (forest)
« on: September 08, 2005, 07:11:32 PM »
I'm having some trouble setting this one up. Your help is much appreciated!

Bird-watchers explore a forest to see which of the following six kinds of birds -- grosbeak, harrier, jay, martin, shrike, wren -- it contains. The findings are consistent with the following conditions:

If harriers are in the forest, then grosbeaks are not.
If jays, martins, or both are in the forest, then so are harriers.
If wrens are in the forest, then so are grosbeaks.
If jays are not in the forest, then shrikes are.

11. If grosbeaks are in the forest, then which one of the following must be true?
a) shrikes are in the forest
b) wrens are in the forest
c) the forest contains both wrens and shrikes
d) at most two kinds of birds are in the forest
e) at least three kinds of birds are in the forest

kmanista

Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #1 on: September 09, 2005, 12:56:08 PM »
If grosbeaks are in the forest, harriers aren't.  If harriers aren't, then neither jays or martins are.
That leaves us with grosbeaks, shrikes, and wrens.

I think the careless mistake here would be to think that we HAVE to have all three kinds of birds.  But the only one we HAVE to have (in addition to the starting grosbeak) is the shrike, per condition (4) -- no jays, so must have shrikes.

Thus the answer is A.

Again, if you want to cross check --

B -- no, we don't have to have wrens.
C -- no, we don't have to have wrens.
D -- no, at most three kinds.
E -- no, at MOST three kinds.

nemo

Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #2 on: September 12, 2005, 07:30:50 PM »
Hmm... another question...

What would be the CONTRAPOSITIVE of the statement "If jays, martins, or both are in the forest, then so are harriers"??

Dinmartin

Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #3 on: September 12, 2005, 07:34:16 PM »
Hmm... another question...

What would be the CONTRAPOSITIVE of the statement "If jays, martins, or both are in the forest, then so are harriers"??

not H---Not J or not M or(neither J nor M)

SanchoPanzo

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Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #4 on: September 12, 2005, 08:23:30 PM »
I'll try:

If jays or martins  --> harriers

contraP.

harriers  --> jays    and    martins

Atlas429

Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #5 on: September 12, 2005, 08:30:58 PM »
Hmm... another question...

What would be the CONTRAPOSITIVE of the statement "If jays, martins, or both are in the forest, then so are harriers"??

not H---Not J or not M or(neither J nor M)

That's actually wrong.

The purpose of the "or both" is to show that the "or" isn't exclusive. In other words, the possibility for the "or" to be an "and"  exsists.
 
So the cp is: ~h -->~j AND ~m

Dinmartin

Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #6 on: September 12, 2005, 08:43:08 PM »
In other words, the possibility for the "or" to be an "and"  exsists.
: how does it exist?  Your explanation is not clear. English is your second language?

SanchoPanzo

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Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #7 on: September 12, 2005, 08:46:17 PM »
In other words, the possibility for the "or" to be an "and"  exsists.
: how does it exist?  Your explanation is not clear. English is your second language?


Atlas429 is saying that this is not an exclusive-OR.



Atlas429

Re: Another Game -- Exam 33, sec 4, #11 (forest)
« Reply #8 on: September 12, 2005, 08:50:07 PM »
In other words, the possibility for the "or" to be an "and"  exsists.
: how does it exist?  Your explanation is not clear. English is your second language?


Let me explain.

In everyday life we think of "or" as exclusive. Coffee or tea. This or that. Meaning we get one but not the other.

On the lsat, this isn't always the case. For instance "jays or martins" means we could have jays AND we could have martins - both at the same time. It's also true we could have just jays or just martins.

However, if the rule said something like "jays or martins but not both", then we know the or is exclusive meaning we can have jays or we can have martins but we cannot have both at the same time.

Get it?