Q21

[polidoroalexandra]

I understand how A, B, C, and, E are incorrect. However, I don't understand why D is correct. Is it because each center MUST have three kinds of material? I don't understand why it couldn't be:

Center 1: glass, tin, news
Center 2: glass, tin, news
Center 3: plastic, wood, news

[ohthatpatrick]

Hey, Alexandra.

Your scenario is perfectly legal.

It just doesn't help us pick an answer or eliminate any answers for this type of question.

Since this question is could be true, it's just asking "Which of these scenarios is possible?"

You're demonstrating that another scenario is ALSO possible.

But to get this question right, we need to
test each choice, and see if it's possible or impossible.

4 impossible wrong answers, 1 possible correct answer.

First, we'd ask ourselves whether we know anything when all 3 groups have exactly 3 things.

I might try to organize which threesomes are likely / possible
- The one with P can't have G.
So it could be PNT, PNW, or PTW.

But wait, PTW would violate rule 1.
If you have W, you gotta have N.

So it would be
PNT or PNW, which you can write as P N W/T

We know G is going to be in the other group, but not P.
So, by the same token, we'd have
GNT or GNW, which we could write as G N W/T

P N w/t
and
G N w/t

One of those will repeat twice, because of the Center 2 = Center 1 rule.

(A) Impossible, because anything in 2 is also in 1.

(B) Impossible, because N is gonna be in all three groups.

(C) Impossible, because Center 2 and Center 1 will have identical groups.

(D) Yup. We could do
PNW | PNW | GNT

(E) Impossible, because Center 2 and Center 1 will have identical groups.