McKinsey Problem Solving Game (Imbellus): Full Practice Guide
Gal Jacobi

Gal, Expert on Game-Based Assessments at JobTestPrep.

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What is the McKinsey Problem Solving Game (PSG)?

The McKinsey Problem Solving Game, also named McKinsey Imbellus, McKinsey Digital Assessment, and Solve, is a gamified test that replaces the previous assessment, PST, in the recruiting process. The PSG consists of two mini-games lasting for 70 minutes and evaluates candidates on five key cognitive abilities.

Only candidates who pass this stage are invited to the next hiring step, the case interviews.

What Skills Does the PSG Evaluate?

The PSG evaluates the consulting traits and qualifications of a candidate and then compares them to a real McKinsey consultant. If the applicant appears similar or better than the actual consultant, they'll pass the test.

Five main thinking skills are being assessed:

  • Critical Thinking: The ability to solve problems by breaking them down into smaller parts.
  • Decision-Making Process: The ability to take in large amounts of information and process it efficiently to make the best possible decision within time constraints.
  • Meta Cognition: The ability to monitor your cognitive processes and improve them.
  • Situational Awareness: The ability to keep track of several tasks or activities concurrently.
  • Systems Thinking: The ability to identify the root causes of problems and possible solutions.

Do All Candidates Get the McKinsey Problem Solving Game?

As of 2024, almost all candidates for nearly all Mckinsey offices receive the Problem Solving Game. The PST, on the other hand, is no longer in use.

Get to Know the McKinsey PSG Format Inside Out

The Problem-Solving Game is sent to candidates once they pass the initial resume screening, making it the second hiring step.

McKinsey has created five mini-games, but you'll need to take only two of them. The most common ones are Ecosysystem Building and Redrock Study, and there are four other less common mini-games that only a fraction of the applicants receive (outlined below).

The time limit for the two common mini-games is 70 minutes, and for the others, it may range between 60 to 80 minutes. Each game will also have a tutorial, which is untimed.

Now, let's dive into each of the mini-games so you'll know what to expect on the test.

Ecosystem Building

The first mini-game you'll need to pass is Ecosystem Building. In this game, you'll be randomly placed in either a mountain ridge or a coral reef scenario.

McKinsey PSG Mountain Scenario Example


McKinsey PSG Coral Reef Scenario Example

Your main objective in this mini-game is to build a sustainable ecosystem using exactly eight species from a collection of 39 species.

To achieve this goal successfully, you must strictly follow these guidelines:

  • Terrain specs: The chosen location in the ecosystem must provide suitable living conditions for all eight species.
  • Calories balance: Each species must be fed with enough calories from food to sustain itself.
  • Food chain continuity: Each species must not be eaten into extinction by its predators.

The gaming platform provides specific information to help you meet these guidelines (some are seen in the game's "guidebook"):

Terrain Specs

Each location in the ecosystem has seven to eight terrain specs. You can choose a location using a pinpoint.

Of these seven or eight specs, only four can be displayed at any given time, using a checklist table in the upper-right corner of the screen:

McKinsey Digital Assessment Terrain Specs Checklist Sample

Now, here's what's crucial about these living conditions:

Each species has specific terrain specs that have to be met. If they aren't met, the species won't survive, and you won't achieve the game's main objective.

Luckily, the species' living conditions usually come in ranges, allowing you to be more flexible with the species you choose for your ecosystem.

Additionally, each species has only two to four terrain specs, when Depth/Elevation and Temperature appear for all species:

McKinsey Imbellus Coral Reed Terrain Specs Example

Knowing that you only need to look at specific terrain specs on the checklist table helps eliminate species or locations that are not suitable for creating a sustainable ecosystem.

Food Chain Continuity

The 39 species are divided into producers and consumers.

Producers are plants and fungi (in the Mountain scenario) and corals and seaweeds (in the Coral Reef scenario). They don't have any calorie needs, so their "calories needed" spec is always zero.

Consumers are animals that eat either plants, other animals, or both. Some consumers are at the top of the food chain and therefore not eaten by any other species.

While creating the food chain, it's important to ensure that no species is eaten to extinction. This can be monitored using the "calorie needed" and the "calorie provided" specs that each species has (shown below).

Calories Balance

Each species has a calorie needed and a calorie provided, as you can see below:

McKinsey Imbellus Species Calories Example

A species lives if its "calories needed" are less than the sum of the calories provided by other species it eats (other consumers or providers).

Furthermore, the species' "calories provided" must be higher than the sum of the calories needed by other species that eat it.


The Main Challenges of the Ecosystem Building Mini-Game

Ecosystem creation is first of all a decision-making game.

You get all the information you need to deliver correct decisions so there's no uncertainty or inaccurate details.

The problem is that you have a vast amount of information to absorb, calculate, analyze, and prioritize. This includes the specs of 39 species, the terrain specs of each location, and eating rules.

Some of the information is irrelevant and is there to distract you or tempt you to make assumptions. In this mini-game, you must not make any assumptions and you don't need to have any environmental, ecological, or zoological knowledge.

So, your ability to make quick and accurate calculations and ignore irrelevant data will have a great impact on your performance.

The preparation course we recommend on this page includes a replica of McKinsey's Ecosystem Building game. It enables you to practice using a like-for-like game experience and learn about every single rule, move, and item in detail. Plus, you’ll master calculation methods and other tactics to ensure the food chain survives in your chosen location.


Redrock Study

The second mini-game you'll most likely encounter is Redrock Study. 

In the game's storyline, your task is to analyze the species inhabiting an island, which includes wolves and elks. The objective of your analysis is to formulate predictions and conduct various calculations, specifically focusing on percentages, by examining data on the evolution of the animal population.

The game has 4 sections:


  1. Investigation 
    You will be presented with a written text that includes tables and graphs. Your task is to sort information and gather valuable data for the following test sections.
  2. Analysis 
    You will be presented with 3 or 4 math problems; each is separated into two parts. You will be given a calculator and a Research Journal to gather information relevant to the questions.
  3. Report
    You will be presented with two types of questions - 
  • 5 written questions regarding your findings in the analysis section
  • 1 visual question in which you will need to choose a graph and use it to show what you found in the analysis.
  1.  Cases
    You will be presented with 6 to 10 questions that are unrelated to the analysis you did so far. 

You will have 35 minutes to complete all four sections, with a short, non-timed break before each one. 


Alternative Mini-Games

As of 2024, the Ecosystem Building game is constant, but the second mini-game may vary in rare cases. This means that there's a slight chance you won't get the Plant Defense mini-game, but rather one of the three we show below.

Disaster Management

In the Disaster Management game, you have to identify what type of natural disaster has happened to an animal population in an ecosystem.

Then, based on the data and information given, you need to choose a different location that will ensure the survival of the ecosystem.

The Disaster Management mini-game has only one objective - the sustainability of the ecosystem, similar to the Ecosystem Building mini-game.

Disease Management

In the Disease Management mini-game, you have to identify patterns of a disease within an ecosystem and predict who will be infected next. You can then use the information given about each species to help you solve the problem.

Migration Management

Migration Management is a turn-based puzzle game. The candidate must direct the migration of 50 animals while helping them arrive at their destination with minimal casualties and with a pre-determined amount of resources.

Plant Defense

Plant Defense is a turn-based mini-game (similar to popular Tower Defense games). Your main objective is to defend a native plant that's located at the center of a 10x10, 10x14, or 12x12 grid from invader species, using defensive resources for as many turns as possible.

This mini-game consists of three maps, and each map is divided into two - the planning phase and the fast-forward phase. McKinsey recommends allocating 12 minutes per map, which makes it 36 minutes in total.

Planet Defence Example

The 36-minute time limit is not fixed though, as it depends on how long it took you to finish the first mini-game, Ecosystem Building.

Many candidates mention that the Plant Defense game is more challenging than the Ecosystem creation. So, keep that in mind while taking the first one and plan your time wisely.

Now, let's take a closer look at the different elements and resources of this mini-game:


Your base is the native plant that you have to defend from invaders at all costs. Once an invader reaches the base, you lose the game.

Note that eventually, everyone loses, and you can't hold your base forever. But the more turns you manage to survive, the better.


There are two types of invaders in the game - Groundhog and Fox. Their movements on the map are the same, and the only difference between them is the terrain type that holds them back (more on terrains below).

Once an invader appears on your map, it will choose the shortest path to reach your base plant. This path will be shown as a yellow arrow.

McKinsey Plant Defense Example


There are three types of terrains in the game:

  • Forest: Slows down the Groundhog for one turn
  • Rocky: Slows down the Fox for one turn
  • Cliff: Blocks both the Fox and the Groundhog from passing this square

Each terrain holds one grid on the map, and you cannot place terrain on a grid that already has another terrain or a defender on it (more on defenders below).


As opposed to terrains, defenders don't just slow down or block an invader, they eliminate it for good.

There are several defenders you can use in the game: Bobcat, Falcon, Wolf, Python, and Coyote.

Note that you won't see all of the defenders at once.

Each defender has two important specs you must take into account:

Range: Each defender can cover a pre-determined number of grids on the map. For example, a Python can cover only one grid, while a Falcon can cover as many as 13 grids.

Damage: Each defender can cause specific forms of damage to an invader's population. When an invader attacks, you'll be able to see its population number and the damage that your defender can cause him. A Wolf, for example, has a damaging impact of 60, while a Falcon has only 20.


The Main Challenges of the Plant Defense Mini-Game

In this mini-game, you have to make decisions based on limited information and face unexpected events (like new invaders from any direction). Also, you must achieve two simultaneous objectives - survive each of the turns separately and for as long as possible.

This is the complete opposite of the Ecosystem Building game, in which you have all the data in front of you, and you have just one objective.

Two things that can help you overcome these challenges are (1) preparing for the unexpected events that will happen during the game and (2) planning low-risk solutions based on your resources (terrains and defenders).

The prep course that we recommend on this page has the closest simulation possible to the actual Plant Defense game. It has the same gameplay, invaders, and resources, and it's based on the same algorithm that appears in the McKinsey Problem Solving Game. This will enable you to learn the most effective tactics to ensure your base plant survives as many turns as possible.


How to Beat the McKinsey Problem Solving Game?

The proven way to beat the McKinsey PSG is by properly preparing beforehand.

There's no way around it. That’s because the mini-games include an immense amount of information, rules, and patterns you must master. And they require you to use tactics and strategies that are not obvious and take time to plan and execute.

All of that is under great time pressure and the high stakes of possibly failing it and losing an opportunity to work at McKinsey.

Now, there are a few practice options you can use to get a better understanding of the PSG and improve your chances of passing it, with the PSG Interactive Simulation being the most accurate one.

McKinsey Problem Solving Game Practice Options

PSG Interactive Simulation

The PSG Secrets simulation is an interactive platform that includes accurate practice for every part of McKinsey’s PSG. It mirrors what the actual game scenarios look like, what each button does, how the logic of the games works, how it generates the data, and more.

It has a full simulation option (two mini-games, 70 minutes), which includes:

  • A full video course in 24 videos and 2h30m of content on Ecosystem, Redrock, and Plant Defense
  • 2 excel solvers for the Ecosystem Game
  • 10 Redrock test drills specifically for the case section
  • 152 page-pdf guide 
  • 60-day money-back guarantee.




Tips to Improve Your Performance on the McKinsey Problem Solving Game

Here are several specific tips to help improve your overall performance on the test as well as tips to avoid any disturbances that could hurt your score:

#1 Sharpen Your Mental Math Abilities

The ability to make fast and accurate calculations can help a lot in this Problem-Solving Game. That’s because one wrong calculation might ruin your carefully built Ecosystem or cause an invader to reach your Native Plant.

There are several free apps and sites, like the renowned Khan Academy, that can help you improve your math skills quickly.

#2 Learn Fast Reading Skills

Mckinsey’s PSG requires you to absorb and analyze a tremendous amount of information under strict time constraints.

Fast reading skills come in handy in this test and can help reduce the amount of time needed to understand the numerous guidelines of the mini-games.

There are certain apps and browser extensions that allow you to practice this important skill, even on the go.

#3 Focus Only on What Matters

Don't get nervous when you first see the immense amount of data on the mini-games. That’s because a lot of the data is irrelevant, and you’ll be only using some particular parameters.

For example, in the Ecosystem game, you’ll only have to use specific species and terrain specs for your calculations, while ignoring others that are there only for distraction.

In the complete PSG Simulation Practice, you’ll see how to remove as much as 70% of the irrelevant data and remain just with the information that matters.


#4 Ignore Outside Information

While taking the assessment, especially the Ecosystem game, try to ignore any outside knowledge and information.

For example, if you’ve learned biology or zoology and you see that your food-eating rules don’t seem logical but the numbers are correct, always go with the numbers.

If you start to rely on previous knowledge, you might get confused and mess up your progress in the game.

#5 Learn to Solve Problems Like a Consultant

The PSG measures your consulting traits and compares them to a model McKinsey consultant.

That’s why learning to think and solve problems like a real consultant can help you pass this assessment.

Two main problem-solving skills you should practice are decision-making in fully controlled situations and with limited information.

Both of these skills can be trained using complex strategy games (examples are mentioned above) as well as practicing with the full PSG interactive simulation.


#6 Cut Down on Calculation Time Using Microsoft Excel

Mental math is an effective way to make calculations in the mini-games.

But as you’re only human, it’s not error-free. That’s why using a calculation tool, such as Excel formulas, can be a great way to make super fast and accurate calculations.

You can use it to gather all the relevant data, arrange it with columns and formulas (even in advance!), and turn the whole process into a no-brainer.

That said, you’ll need to use another monitor (preferably with a different browser) or another laptop since the assessment’s platform will take over your entire screen.

#7 Prep Your Hardware and Internet Connection

The last thing you want during the assessment is a “blue screen of death.”

Blue Screen of Death Example

It may happen if your hardware is not strong enough, since the McKinsey PSG is pretty demanding in its system requirements.

Any computer that is more than five years old or without an HD screen will likely encounter lags and performance drops.

Also, you must have a fast and stable internet connection. If you get disconnected in the middle of the test, you might need to start all over again or even reschedule for another testing date.

PSG Scores

The PSG scores are divided into two types -

  • Product score - the final outcome of your performance
  • Process score - the efficiency (time and number of clicks) of your performance 

If you get the PSG Practice Simulation, you’ll have a mock grading system that monitors your results and behavioral patterns.

This will allow you to track your progress while you practice for the test and see which areas demand improvement.

Why Did McKinsey Develop the Problem-Solving Game?

McKinsey created the Problem-Solving Game as an unbiased way to identify candidates from around the globe with strong cognitive abilities. The former assessment, Problem Solving Test (PST), was less challenging for candidates who were familiar with standardized tests, such as SAT and GMAT, or used the numerous mock tests found online.

The PSG, on the other hand, is supposedly crack-proof. That's because it takes into account the approach you use to solve the problems and not just the final solution. This seemingly removes any lucky guessing and shortcut techniques that were common on the McKinsey PST.

While on the PST you had just your final score, on the PSG your score is comprised of dozens of scoring criteria apart from your final result, including mouse movement, keystrokes, and clicks.

McKinsey can analyze these factors for every recorded candidate, which allows them to compare candidates more fairly.

What Does Imbellus Mean?

Imbellus is a company that creates immersive simulation-based assessments to assess cognitive processes. To develop a new testing format for the McKinsey recruitment process, they've teamed up with McKinsey consultants and UCLA Cresst psychologists.

In 2020, Imbellus was purchased by Roblox, an online gaming platform, to help sharpen its recruitment practices.


This was an in-depth prep guide for the McKinsey Problem Solving Game. It gave you an overview of the different mini-games, explained their main challenges, and offered some useful solving tips.

Additionally, you saw the best ways to prepare for the assessment, when the PSG Practice Simulation being the most realistic and accurate one.


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