McKinsey Problem Solving Game (Solve) Explained - with Footage -

McKinsey Problem Solving Game (Solve) Explained – with Footage

MConsultingPrep Official Channel
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(Also includes the NEW MINI GAME “Redrock Study Task”)


McKinsey Problem Solving Game (PSG), Imbellus Game, Digital Assessment, or – as of late – McKinsey SOLVE – all of these terms refer to the same pre-interview screening test employed by McKinsey, starting from 2020 as a replacement for the old McKinsey PST.

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Hope to see you in the next video!


0:00 Intro
0:52 Part 1: What is the PSG?
3:08 Part 2: The mini-games of the PSG
4:39 Part 2.1: Mini-game #1 – Ecosystem Building
12:14 Part 2.2: Mini-game #2 – Plant Defense
19:20 Part 3: Q&A
23:22 Outro


  1. Promised myself to write a summary after completing the PSG and here it's :
    I got 1) ECO System 2) Red rock cases

    Eco system: You should focus on building bottom- Up as it will give you more options to choose producers from, Be careful that it's not pyramid structure, The most important thing is The animal with highest calories needed eats first, also prioritize selection based on highest calories provided and less needed.
    some animal are omnivores meaning it can eat producers and another animals aswell.
    what worked was 3-4-1, Animation in the end shows sustainability of ecosystem (what it shoes survived), it didn't show all of animals (only 4 out of 5)

    Redrock: very hard, not to be taken lightly, it's 10 cases the first two will take 60% of the remaining time of the 2nd part (Yes, even if you finish eco system earlier which i did by 10 minutes, time won't be transferred to 2nd part)
    First case was 2 packs of wolves which needs to be relocated (a lot of formulas to be prepared on the spot, Keep extra papers on hand), 2nd case was the same.

    I can't say much about redrock as it was overwhelming, took me in the first case around 15 min and i had like 20 min for 9 cases, Will update whether i get selected or not.

    It's a good experience overall.

  2. I just did the test today, does anyone knows how long to get the results? I did the ecosystem and the redrock game

  3. Hey Kim , can you please provide me your email? I would like to get in touch with you


    I took the test today and noticed that the second section was different from what was shown in the video. While the video was helpful for the first section and I was able to finish it in 10 minutes, I found the second section confusing. It was a case study test about the Redrock project, and I spent a lot of time writing down all the study information on an excel sheet, thinking it was necessary. As a result, I ran out of time and missed question 3 in the case question section.

  5. Thank you for the tutorial!! Was an amazing explanation. Although I was not given the plant defence game and something else was there to replace it.

  6. I just finished my game a few moment ago and this video has been exremely helpful!!

    Game 1 Ecosystem: thanks to this video and your blog I was totally prepared and jumped right into it. I started bottom up and categorized the providers into 3 groups based on temperature and elevation (the factors that have varied between the animals). I firstly chose the group that produced the most calories but quickly realized that I cant find a good match with the next group of animals in the food chain so I went with the second producers group. In the end I had 3 providers, 3 regular animals and 2 predators.

    Game 2 Redlock: this is the game that Kim mentions in his blog, a relatively new game so I couldnt prepare for this one as much as for the ecosystem. The game has 2 parts: study and cases. Study is where you get a text with highlighted data and then choose the data which is relevant for your research. It was very intuitive. The second part is made of 10 mini cases – some of the cases take less than 30 sec to solve. They involve choosing the right charts to represent your data, simple growth calculations, reading the tables. Most of the data thats given is pretty useless so I recommend to first read the question which is usually at the end of the case and then look at the data presented. You’ll be much faster when you know what you are looking for.

    General: I had a second laptop next to me with excel opened but honestly I didnt need it much. I only used it for adding and subtracting the calories in the first game. But I used paper to collect data for animals (I drew a quick tables for providers to organize the animals better) and to draw my food chain pyramid which was really helpful. For the second game I didn’t need anything – the calculator was given in the game.

    All in all this was my first time playing the game and one of my first consulting assessments so I really want to thank you Kim for making these videos! Discovering your channel was pure blessing!
    To all the other candidates good luck with the game! And don’t stress about it, look at it as it actually is – a game. It will be much more engaging doing so 😄

  7. please, could anyone help me with a clean strategy of choosing location in ecosystem?

  8. Kim, can you do an updated video on RedRock? There's barely any info online and many people are saying they are getting 10 cases.

  9. Hi guys! Completed the test few days ago, and what can I say… firstly, this video was very beneficial! I passed ecosystem game easily because I had the second excel opened and used the tips mentioned here.

    Regarding second part, they have change it. So, there is no plant defense game. Instead you are given some studies, cases and calculations.

    I also wanted to ask those who has passed, did you receive the email confirmation right before the test? Because I did not received any and now I am bored.

  10. Hello everyone! Test completed few minutes ago. Ecosystem + Redrock. For the ecosystem, the bottom-up strategy is definitely the best because the structure is not a pyramid in any case. This means that you can have an APEX animal even on the second level. I think I did it well but I didn't have time to double-check. Another piece of advice, you have 29 minutes to complete the game, use them because the minutes aren't cumulative through games. Redrock: time is challenging. I arrived at the last case study with no time left. More or less, this game is all about percentages and data selection. The visualization part is quite easy. Now I'm waiting for the result. I'll touch you back.

  11. Guys, I have a few questions about the Ecosystem: e.g., when you selected your PRODUCERS with depth/temp. 61-90 and 25-29, respectively, then the next group (until the end) you must have in the same range – depth/temp?????

    I did that, and while using a bottom-up strategy, I constantly have the same issue – at least one animal has insufficient calories provided for the next animal in the food chain …

    Can each level be taken from different depths/temperatures????

    What if one animal doesn't survive? Is it directly a fail??

    Did you use the approach of looking at the “eaten by” specs – while selecting the next group of animals/apex? ??

    I’d appreciate any suggestion, pls

  12. Hi everyone…have a test in next couple of days. Can really use your help / advice with following queries:
    1. Where can i find the link for the excel for capturing the information for the ecosystem building section?
    2. Also can someone tell me if we need to do trial n error to find a sustainable location or there are fixed set of locations in the ecosystem section that we need to test against the species identified as a part of food chain?

  13. Hi Kim! Are you planning to update the video soon with the new game redlock? Really liked your insights on the ecosystem and plant defence game.

  14. Does anyone get more than one possible (sustainable) ecosystem?

  15. I bought the PSG simulation game for my Mckinsey assessment. Let me know if anyone wants the Mconsultingprep PSG simulation game for a reduced price.

  16. Can anybody tell me where can i find the note template? checked all the links in the description. Thanks in advance

  17. Its a great video, ive ended the test today (14/05/2023), in Sao Paulo, Brazil. First there was only 35 minutes to the first ecosystem part. I didnt care about the time, cause i thought (as ive readed in the foruns), that there was 71 minutes for us to manage. After 35 minutes (with my incomplete ecosystem), the test stopped the first task and took me to the second. I got angry cause of it, and couldnt focus to end the second one (i closed the laptop). So, I didnt pass.

  18. You said that the rule is that the current calories provided determines who eats first. However, in your example the snake eats before the fox. Hence, either the original calories provided determines who eats first or the fox should have eaten first. Can someone help me with understanding this?

  19. just took the test a few minutes ago. The ecosystem task went smoothly but the second part was unexpected. it was a case study with studying a report, doing analysis, answering 10 cases, and more(didn't get to the last part due to time constraints). I don't know if this is the new structure but for those who are going to do the test anytime soon kindly familiarize yourself with case studies that have numerical reasoning. I encountered lots of percentage calculations.

    Generally, I don't think I did well considering the second part was awful. wishing all the best to anyone preparing to take it.

  20. Hello guys I just took the assessment, but didn't see the pass or not pass sign … How do you guy know whether you pass or not?
    And thanks for the video on the ecosystem it really helps I really hoped you had video for redrock too

  21. What happens when you have an apex predator that eats both a predator and also herbivore? Will the apex predator still eat the animal with most calories produced (in this case the herbivore)? If yes, then the apex predator and predator will both be in the same hierarchy given that they both eat animals below

  22. I'm just from doing the test! Thanks so much for this tutorial.
    The most useful intel I got from the tutorial is:
    1. Using a pen and paper instead of excel. Personally, I write faster.
    2. Bottom up strategy. Producers first.
    3. There's a lot of noice in the data. Find the most relevant, using two data points.
    4. Don't obsess over calorie calculation. Ensure you have the 8 species first, create a rough pyramid structure with the template shown in this video and estimate the calories. If you have more than 10 minutes left after selecting the location, then you can do the calculations.
    I've found it very helpful. Most importantly, the comments people left are even more helpful since it provided more recent info for me. I didn't bother with the Plant defence section since I was sure they'd bring the RedRock study as people stated in the comment section. The ecosystem builder section is definitely easier than the redrock bit. I'd advise you polish up on percentage calculation and probability. I guess you shouldn't be worried about completing the study section, I haven't come across someone who has. I think it's more useful to do the ones that you do correctly.

  23. If the test shows task completed, does that mean, i was able to create a successful ecosystem?

  24. Pro tip: do watch this video just before sitting for the test.

  25. Many thanks for such an insightful video, i just completed the test, and this video was really helpful.

  26. Where is the note template described in the video?

  27. Hello guys. I passed the PSG yesterday. I never comment on YouTube but this video + the comments gave me a lot of information, so my turn now:

    1/ I bought the MConsulting Prep game. The design is almost the same as the real game and is very useful for training and understanding PSG.

    2/ For the ecosystem, it's almost the same interface, the only difference being that the "calories needed" and "calories supplied" columns are opposite in McK's.

    3/ Still for the ecosystem, the 3 producers with the highest calories didn't allow me to obtain an 8-species ecosystem, so I opted for the second group of producers with the highest calories and it worked perfectly, so beware, the group of producers with the highest calories isn't necessarily the one to take. It's important to take this eventuality into account!

    4/ Selecting the location is super-easy: just select temperature, ph, wind speed and elevation. What's more, you just need to find a location that matches elevation and temperature, as ph and wind speed will always fall between the rows, no matter which location you select.

    5/ I didn't get the plant defense but the Redrock study. As it says in the MConsulting Prep, you can guess the start when you have a 31-minute stopwatch, as these are 2 separate stopwatches and not a single 71-minute one as for the ecosystem + plant defense. It would appear that the Redrock study is now replacing Plant Defense, but this needs to be confirmed with other participants.

    6/ Redrock's study is 10x easier than those given in MConsulting Prep. These are basic calculations on the growth of variations, but beware of time. I didn't have time to finish (I was on the last question and still doing calculations when the page closed automatically).

    7/ the spreadsheet is useful for Redrock because some questions ask for the median/node/average of 31-column tables, so easier with a spreadsheet 😆

    Good luck to you all!

  28. I did the PSG test yesterday (got Ecosystem and Red Rock Study games, separate time clocks) and wanted to share my experience since the other comments helped me quite a bit. My preparation basicially began around 4 hours before the exam and mainly consisted of watching this video twice and look through the comments. I saw preparation tools/guides etc. online particularly for the PSG which sold for over 200 USD which in my opinion are not necessary and rather a waste of money but hey, if money isn't a problem it certainly wouldn't affect your performance negatively. Here are some details regarding the games:

    1. Ecosystem (coral reef): As often suggested in this comment section I took the bottom-up approach and started finding the group of producers with the same depth and temperature requirements which provided the most calories. Then with a prepared excel sheet on a separate laptop I listed all the species fitting the required conditions my producers needed including the most important details. From there on I just prioritized the species with higher cal provided/lower cal needed and made sure that they eat/get eaten by the other producers/species. Though it can become pretty messy with all the data it generally is quite straightforward and after around 30min I had a 3-3-1-1 working ecosystem and got the three green checkmarks after completing it. I highly recommend using either a pen and paper or excel sheet to gather all the compatible species and their most important info. Also be aware that certain species might have similar names (e.g. "common angelfish" and "dark blue angelfish") so don't get them messed up.

    2. Red Rock Study: I didn't prepare at all for the Red Rock Study and pretty much had no idea what it is about. The good news is that you don't really need to prepare for it. I had two parts with the first one being a study you conduct where you will be provided with some information and questions mainly requiring small calculations and a final report summarizing your findings. You will be provided with a "Journal" which you can use to save certain information with drag and drop from the report provided to answer the questions. Make sure to get all the information before going into the final report because you won't be able to go back. This is not the case for the questions, there you can go back anytime. The second part was 6 small cases/questions unrelated to the study where you just have to conduct some basic calculations. Generally it's rather simple and I would argue that if you are familiar with a bit of math there's no need to prepare for the Red Rock Study.

    I think I did pretty well throughout the whole assessment but I'll let you know as soon as I hear back from recruitment.

    Let me know if you have any questions, good luck! 🙂

  29. I think the BEST strategy is to built the chain from the top top the buttom. It allows u to select predators with the same amount of of calories provided

  30. Quick question! In the plant defense game, if you put an animal over a terrain that was there from before, does the animal use it's damage? In the video it looks like the population didnt decrease, so I'm guessing that it is unwise to put an animal over a terrain? Thanks in advance to anyone who answers!

  31. Hi Kim, Thank you for these wonderful videos, I have a doubt in the example u gave for ecosystem building, Why cant the level 1 tiger eat 1000 calories each from snake and fox so that both of them survives?

  32. Question – the calories provided determines the eating order of the organisms – Is this the original calories provided or the most recent after having been eaten?

  33. Hi, I am currently planning to take the test and what you talked about on the detailed rule#2 @17:10. can you clear it up about the turn that a defender takes. Thank you

  34. Why in Ecosystem implementation does the mouse eat grass and mushroom equally while the grass can provide enough calories?

  35. Hey, just finished my PSG some time ago, got ecosystem and redrock case study, apparently that's the new trend these days eh?
    For ecosystem there's nothing better than the comments and the guide given here, got the 8 species, done!
    Redrock was lengthy af, took so much time, wasn't able to solve the cases, feeling disheartened. Hoping for the best.

  36. Thank you so much for this tutorial.
    Just took the PSG. The ecosystem was easy thanks to this video and the comments. The second was redrock. In a nutshell the redrock tests your maths skills especially word problems and analytical skills. I was unable to finish the redrock though but it was a good experience overall.

  37. Why can't the tiger eat 1000 from snake and 1000 from fox ?

  38. How can i download the excel template for the ecosystem game? Please help me

  39. Please at the end of the ecosystems, i saw alot of animals and a plant, i even saw rabbits. Basically most of what i picked, they were on the field. What does that mean..

  40. Hi. Can you please explain the fourth rule again in the ecosystem . i am unable to understand it . thanks in advance

  41. The Eating Rule says "Eat the one with most calories provided". Does that mean that your species can now eat from any food source ? As the eating rule does not seem to explicitly limit what is being eaten. Does anyone have an answer?

  42. I just took the test, comments here made the ecosystem part relatively easy. However, red rock part was terrible for me. Looking back, I panicked a lot and couldnt figure out what was being asked clearly. If I was able to understand what the question meant I think I could solve the math, it was basic calculations expected in case interwievs. Overall, I think I should’ve looked into the red rock before taking the test. I don’t expect a positive outcome, yet I will update my comment if it is positive!
    Most important take away from my experience would be to prepare properly beforehand (I only had couple hours.) and stay calm during the whole assesment.

  43. Hi, I am confused about the terrain specification part. Do you self-select a location at the start? Do you see which variable is changing and use it to group the species in 3 groups each? Then proceed to look at finding producers within the group that meets the specifications of the chosen location with highest calories provided and do the bottom up approach? Thanks!

  44. When you mention only depth & temperature are relevant, what about who eats who? Since it is essential for the chain to work, isn't it? Thanks!!!!

  45. Hello guys, I thought I'd share my experience of the game since many of the comments here helped me prepare.

    I got ecosystem and redrock study.

    1. For ecosystem I used bottom to top approach 3,3,2. At the end I got 3 green ticks. It took me 35 mins, I used a pen and paper. I never used an excel sheet. Only depth and temperature matter don't worry about the rest. Use a mouse. Keep calm. It's quite easy. You got this.

    2. For redrock I had redrock plus 5 other case studies making a total of 6. I only managed 4. I didn't finish. My advice for redrock WRITE DOWN EVERYTHING! You won't be able to go back and get more data. Don't spend too much time overthinking, time runs out quickly.

    My timeline.
    Email for interview prep came 12 days later

    I hope this helps.

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