Self-study
Among small- to medium-sized marine mammals such as seals and dolphins, the longer an animal can stay submerged during a dive, the greater the depth the animal can reach. ████████ ███ ████ ██ ███████ ██████ ████ ████████ ███ █████ ████ ███ ████████ █████ ███ ████ █████████ ██████ ████ ███████ █████ ████
Stimulus Summary
Fact 1: Among small-to-medium-sized marine mammals, the longer an animal can stay submerged during a dive, the greater the depth it can reach. This means submersion time and diving depth go hand-in-hand. If we know which of two animals dives deeper, we also know which one stays submerged longer, and vice versa.
Fact 2: Dolphins can dive deeper than northern fur seals. Since depth and submersion time go together, we can also infer that dolphins stay submerged longer than northern fur seals.
Fact 3: Elephant seals can stay submerged longer than Weddell seals. By the same reasoning, we can infer that elephant seals can dive deeper than Weddell seals.
Here's what we know:
🌊 surface
🦭 N. fur seals
🐬 Dolphins
?
🦭 Weddell seals
🐘 Elephant seals
↓ deeper / longer submerged
Keep in mind that we don't know how the pair on the left compares to the pair on the right.
Anticipation
This is a "could be true EXCEPT" question, which means four of the five answers could be true and one must be false. We're looking for the one that must be false.
Since we know the ranking within each pair but not across pairs, most answers that only make cross-pair comparisons can easily be true. The answer that must be false will force a contradiction with the orderings we've already established.
25.
If the information above is █████████ ████ ████ ██ ███ █████████ ██████████ █████ ██ ████ ███████
a
Dolphins can dive ██ ███████ ██████ ████ ███████ █████ ████ ███ ███ ██ ██████ ██ █████ ██ ████████ █████ ████
This says elephant seals dive deeper than dolphins, which dive deeper than Weddell seals. Here's one order showing that's possible (the N. fur seals don't have to be at the top; they can go anywhere above dolphins):
🌊 surface
🦭 N. fur seals
🦭 Weddell seals
🐬 Dolphins
🐘 Elephant seals
↓ deeper / longer submerged
(A) could be true and is wrong on this EXCEPT question.
b
Weddell seals can ████ █████████ ██████ ████ ████████ ███ █████ ████ ███ ████████ ███ ████ ██ ███████ ██████ ████ ███████ █████ ████
This says Weddell seals stay submerged longer than N. fur seals, and that dolphins dive deeper than Weddell seals. That means dolphins dive deeper than Weddell seals, which dive deeper than N. fur seals. Here's one order showing that's possible (elephant seals don't have to be at the bottom; they can go anywhere below Weddell seals):
🌊 surface
🦭 N. fur seals
🦭 Weddell seals
🐬 Dolphins
🐘 Elephant seals
↓ deeper / longer submerged
So (B) could be true and is wrong on this EXCEPT question.
c
Weddell seals can ████ ██ ███████ ██████ ████ ████████ ███ ███ ███ ████ █████████ ██████ ████ ████████ ███ █████ ████
So Weddell seals dive deeper than dolphins, and can also dive deeper than N. fur seals (because they can stay submerged longer than N. fur seals). Here's an order showing (C) is possible:
🌊 surface
🦭 N. fur seals
🐬 Dolphins
🦭 Weddell seals
🐘 Elephant seals
↓ deeper / longer submerged
So (C) could be true and is wrong on this EXCEPT question.
d
Northern fur seals ███ ████ █████████ ██████ ████ ████████ █████ ████ ███ ███████ █████ ███ ████ ██ ███████ ██████ ████ ████████ ████
(D) has two parts. Let's take them one at a time.
Part 1: Northern fur seals can stay submerged longer than elephant seals. We already know elephant seals stay submerged longer than Weddell seals, and dolphins stay dive deeper than northern fur seals. Here's the order implied by Part 1:
🌊 surface
🦭 Weddell seals
🐘 elephant seals
🦭 N. fur seals
🐬 dolphins
↓ deeper / longer submerged
Part 2: Weddell seals can dive deeper than dolphins. But...how? Weddell seals are at the very top (shallowest) and dolphins are at the very bottom (deepest). There's nowhere to move Weddell seals below dolphins without leading to a contradiction. That's why (D) must be false and is the correct answer on this EXCEPT question.
e
Northern fur seals ███ ████ █████████ ██████ ████ ███████ █████ ████ ███ ████████ █████ ███ ████ ██ ███████ ██████ ████ ████████ ███ █████ ████
This means elephant seals dive deeper than N. fur seals, which dive deeper than Weddell seals. Here's one order showing (E) is possible (elephant seals don't have to be at the bottom; they can go anywhere below N. fur seals):
🌊 surface
🦭 Weddell seals
🦭 N. fur seals
🐬 Dolphins
🐘 Elephant seals
↓ deeper / longer submerged
So (E) could be true and is wrong on this EXCEPT question.