Imbellus Ecosystem: Does everyone endup with 8 surviving species? Does the correct answer always exist?

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New answer on Aug 17, 2022
5 Answers
Anonymous A asked on Aug 16, 2022

Just finished the official PSG, and had only 7 species surviving. Do all games have the correct answer? Or are some games impossible to get 8 species? Never heard of this scenario before. Is it certain that all games are solvable?

1. What I did before the actual PSG:

  • I prepared rigorously with Francesco's videos and the MC Simulation for 3 days to perfect every detail with a friend.
  • By the end of my preparation, we had optimized our framework (MECE+efficient) and details to every click.
  • I could solve all simulations within 15mins, with at most 20 species opened/checked and less than 40 mouse clicks. (Stable performance during ~10 mocks)
  • I pre-printed sheets for each stage of analysis to decrease human error and increase efficiency.
  • And the list goes on…


2. What happened during the actual PSG:

  • As planned, I divided the height into 3 categories based on total calories from producers.
  • I started with the optimal height with the most calories from producers. Then I realized that only 7 could survive with bottom-up and top-down approaches. (Re-examined with my note afterward with all combinations, quite certain.)
  • Then I went for the second height, and again only 7 could live. In one combination, the 7th prey had 2600 cal provided, while its only predator had 2600 cal needed. In the end, I went with this solution before running out of time. (Less certain about the second height, due to the time limit I did not record every piece of data.)

3. So this can happen? Or is it certain that the game is solvable, I just did not reach it?

  • Wanna hear if anyone had a similar experience, or is it guaranteed that a right answer does exist?



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Content Creator
replied on Aug 17, 2022
McKinsey | MBA professor for consulting interviews

I have never heard about an impossible 8-species ecosystem to create, but I confirm candidates get invitations even without being perfect on this game, so..finger crossed!


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Content Creator
replied on Aug 17, 2022
#1 rated McKinsey Case and PEI Coach | 5 years at McKinsey | Mentorship Approach | 120+ McK offers in 18 months

Hey there,

Very likely that McKinsey introduced these changes as I am getting similar reports (same as that the plant defense is getting replaced as well with a new game).

It makes sense since they have been adjusting the game ever since they launched it. I have written and published the first guide for it in Nov 2019 already and have gone through countless bigger and smaller iterations since then.

Based on your prep, I would not worry about it.



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replied on Aug 17, 2022
McKinsey San Francisco | Harvard graduate | 5+ years of coaching | DISCOUNTED SESSIONS Sep 2022 | Free 15 min intro call


I haven't heard of such a scenario, but it is probable that they may have changed something in the game so that some scenarios only have 7 species surviving now, particularly as others here seem to have heard of such experiences too. In any case, I wanted to reiterate Antonello's advice that you don't have to be perfect on the game to get an interview offer, so I wouldn't worry too much about it given that it's happened now. Best of luck!

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Content Creator
replied on Aug 17, 2022
MBB | 100% personal interview success rate (8/8) and 95% candidate success rate | Personalized interview prep

Hi there,

This is really interesting.

I honestly haven't heard of this yet, but it sounds like you were well prepared and really considered all scenarios.

Here's what I do know: nothing is ever a sure thing with these interviews. They are always changing the games, the format, the questions, etc.

So, it does sound like they may have changed it a bit to allow for only 7.

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Anonymous B replied on Aug 17, 2022

I just took it now and had a similar experience, I’m not really sure if all 8 species could survive I only got 7 to survive 

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Anonymous A on Aug 17, 2022

Some of my friends who took the test a few hours before had the same problem. A few said that they had the answer by the second height, but none got one from the first height, especially if one producer is eaten by nothing.

Antonello gave the best answer


Content Creator
McKinsey | MBA professor for consulting interviews
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