The plane that departs second could be any one of exactly how many of the planes?

Stephanie on February 5, 2019

Question

Can I see an explanation for this question without using the GURU method?

Replies

Ravi on February 5, 2019

@Steph,

Happy to help.

The best way to answer this question is to make sure that your game
setup is solid. This is a question that rewards you for doing work up
front and can be answered very quickly if you've made the necessary

We're told Flyaway owns two planes: P and Q, and Getaway owns exactly
three planes: R, S, and T.

F: P, Q
G: R, S, T

Each plane makes one flight.

Rule 1 says only one plane departs at a time.

1) _ _ _ _ _

Rule 2 says each plane makes either a domestic or an international
flight, but not both.

2) i - >/d
d - >/i
/i - >d
/d - i

Rule 3 says P makes an international flight

3) Pi

Rule 4 says Q and R make domestic filghts

4) Qd, Rd

Rule 5 says all international flights depart before any domestic flight

5) i-d

Rule 5 is crucial because it allows us to make some inferences. With
Rule 5, we know that Pi must go before both Qd and Rd

Rule 6 says any Getaway domestic flight departs before Flyhigh's
domestic flight.

Rule 6 makes us know that Rd must go before Qd, so now we have

Pi - Rd - Qd

We only have 2 pieces left to map, S and T. We can make two separate
boards that show what would happen if S and T were i or d,
respectively. If S and T are d and i or i and d, we can just use the
parts from each setup that have them in those places and combine them
into a new map. For simplicity, it's best to just write out the two
separate scenarios with S and T both being i or d so that we have less
clutter on the page.

If S and T are both i, then rule 5 triggers, so we know that they must
both go before Rd, which must go before Qd

Pi - Rd - Qd
Si - Rd - Qd
Ti - Rd - Qd

If S and T are both d, then they will be on par with Rd but will still
be before Qd because they are Getaway flights and all Getaway domestic
flights go before Flyhigh's domestic flight

Pi - Rd - Qd
Pi - Sd - Qd
Pi - Td - Qd

In both of these worlds, Qd is last, so we know that Qd must go 5th on the board

_ _ _ _ Qd

The question asks us how many planes could depart 2nd. We know Q is
out, so (E) is out as well, giving us four answer choices left.

Looking at our scenarios, in our second one we see that Rd, Sd, and Td
would all go after Pi but before Qd. However, Rd, Sd, and Td have no
order hierarchy with respect to each other, so this means that any of
them could go 2nd after Pi. This means that at least 3 of the game
pieces could go 2nd.

Now, let's see if P could go 2nd.

In our first scenario, Pi, Si, and Ti all have to go before Rd - -Qd.
However, there is no hierarchy of order with respect to Pi, Si, and
Ti, so Pi could go second after either Si or Ti. This means that 4 of
the 5 pieces could go 2nd, so (D) is our correct answer.

Does this make sense? Let us know if you have any more questions!
6)

Stephanie on February 9, 2019

Thanks! Makes sense.

Ravi on February 9, 2019

@Steph happy to help!