Law School Discussion

Another Game -- Exam 33, sec 4, #10 (forest)

nemo

Another Game -- Exam 33, sec 4, #10 (forest)
« on: September 08, 2005, 08:10:13 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.

10. Which one of the following pairs of birds CANNOT be among those birds contained in the forest?
a) jays, wrens
b) jays, shrikes
c) shrikes, wrens
d) jays, martins
e) shrikes, martins

kmanista

Re: Another Game -- Exam 33, sec 4, #10 (forest)
« Reply #1 on: September 09, 2005, 01:51:47 PM »
This is another where I'd just check each answer in turn.

A first -- if we have jays, then we have to have harriers, according to condition (2).  If we have wrens, we have to have grosbeaks, according to condition (3).  Oops, condition (1) says we can't have both harriers and grosbeaks.  So we can't have both jays and wrens.  That was easy.

If you want to / have time to cross check :

B is ok -- condition (4) doesn't say we can't have both.
C is ok -- we can have shrikes, wrens, and grosbeaks, and not have jays, martins, or harriers.
D is OK -- we can have jays, martins, and harriers, and even add shrikes -- just not wrens, because of condition 4.
E is ok -- we can have shrikes, martins, harriers, and even jays, as long as we don't have wrens.