Q7

[mchuynh]

For question 7, is the answer E because all we know is that MH are in and GW are out? And we can't conclude whether or not there are at least two other kinds of birds in the forest because we don't have enough information? Thanks

[bbirdwell]

MH are in, GW are out. J and S cannot both be out. Maybe one of them is in and one of them is out, maybe both of them are in.

Therefore, we know that at least ONE other bird is in the forest, and at most, two.

[michellemcvaney]

I don't understand why E is the answer. This is how I am interpreting this...if -J then S, which means if -S then J. So how can they BOTH be an option to be selected? Could someone please elaborate on this for me. Thank you!~

[timmydoeslsat]

To say ~J ---> S is to say that at least one of those two variables must always in the game.

We can have both be in. What happens if we have J? We do not know from that statement. What happens if we have S? We do not know from that statement.

That rule triggers when one of those variables are out.

[hnadgauda]

I don't think I'm understanding this question...H and M are already in the forest. J only, S only, or both J and S can be in the forest. So this means that there are at least 3 birds in the forest at a time correct? I am saying this because J and S can't be out of the forest at the same time and if you're not out of the forest, you're in the forest.

How is it true that there are at most 2 kinds of birds in the forest (Answer choice E)?

I think I'm missing something very important... Can someone please clarify?

[ohthatpatrick]

Beating an answer choice in MUST BE TRUE means that you have a counterexample in mind.

(A) is wrong because it could be MHJ or MHJS. In both cases, S is not the ONLY other bird.

(B) is wrong because it could be MHS or MHJS. In both cases, J is not the ONLY other bird in the forest.

(C) is actually a MUST BE FALSE. It will never be true in this game that J and S are out, because of rule 4.

(D) is wrong because it could be MHJ or MHS. In both cases, there are not AT LEAST TWO more birds in the forest.

(E) is correct because the most birds we could have in the forest would be MHJS. Since we already know about MH, there are AT MOST two other birds in the forest.

"At most 2 others" = 2 more, 1 more, or 0 more

All our potential scenarios -- MHJ, MHS, MHJS --- are either 2 more, 1 more, or 0 more.

To prove (E) wrong, you'd need a counterexample where there are THREE other birds in the forest. MH _ _ _

Another way of expressing (E) is saying
(E) The IN column has a maximum of four birds.

Another way of expressing (E) is saying
(E) At least two of the six birds are OUT.

[VendelaG465]

I'm lost on the S& J rule. How can BOTH be in ? If S is out, then J is in. & if J is out then S is in. You're being forced to pick either or...?

[ohthatpatrick]

The rule doesn't even apply if they're both IN.

You can't break a rule, if it doesn't apply to current situation.

Consider a rule that says:
"If it's Tuesday, then you have to be wearing blue pants."

Now let's look at Sharon's outfit to see whether it complies with the rule. Also, let's say that today is Friday.

What do we need to check to see if Sharon's outfit complies with the rule?

NOTHING! The rule is irrelevant. Today is Friday, not Tuesday, so the rule doesn't say ANYTHING about what Sharon should be wearing.

If S and J are in the forest,
and a rule stipulates,
"If S is NOT in the forest" ...
we stop reading.

S is in the forest. This rule is irrelevant. Simple as that.

IN/OUT games are full of these rules that will fool your eyes into thinking they're an EITHER/OR.

"F and G cannot both be in the forest" looks like
F --> ~G
G --> ~F

Does that mean it's either/or? One's IN, one's OUT?

No, they can both be out. If F and G are out, and we read a rule that says
"If F is IN .... "
we stop reading.
It doesn't apply to our current situation, so it's meaningless.

Make sure as you read your conditional rules, you're making your brain say, "IF the left side is true".

If the left sides isn't true, the rule instantly evaporates. You don't need to consider the contrapositive (because it's one and the same thing).

If the trigger of a rule doesn't apply to the current situation, then it's impossible to break that rule with the current situation.