How to answer Top Guesstimate Questions in an interview

Guesstimate questions are very common for consulting, data analytics or product management interviews. If you’re new to this and feeling a bit lost on how to answer them, you’re in the right spot! I’ve got your back.

As someone who values your unique journey, I’ve crafted this article specifically for you – a comprehensive guide to help you approach and master Guesstimate questions using your unique strengths and skills.

Purpose of asking Guesstimate questions:

The main purpose of Guesstimate questions is to test your problem-solving skills, creativity, and ability to think on your feet. I understand that these questions can be daunting, but remember, you possess the skills needed to excel. When I started with solving the guesstimate questions, I thought like the main purpose of guesstimate questions is to come up with a correct number. But that’s not true. The main purpose of guesstimate questions is not about arriving at a perfect answer but rather its all about demonstrating a structured approach, logical reasoning, and effective communication.

Tips to approach Quantitative Guesstimate Questions in an interview

Alright! I hope you got the essence of asking guesstimate questions. Lets now decode the approach to answer guesstimate questions in any interview.

Let’s go through the process of estimating the total number of tennis balls that can be fitted in a school bus. Even though it is a challenging task, but with a structured approach, it can be tackled effectively during the interview.

1. Break complex problems into small chunks: I’ll help you break down complex problems into small chunks or manageable parts, empowering you to approach any question with a methodical mindset.

For example, consider estimating the total number of tennis balls that can fit in a school bus. Break down the problem into manageable components: the size of a tennis ball, the interior space of a school bus, and any factors influencing how they fit. This step sets the foundation for a structured approach.

2. Realistic assumptions for Guesstimate Questions: Explore scenarios involving numbers, such as estimating the number of cars passing through a toll booth in a day. Learn to make realistic assumptions, such as the average number of cars passing per minute and the operating hours of the toll booth. Practice quick, back-of-the-envelope calculations to arrive at a reasonable estimation.

For example, While estimating the average size of a tennis ball. Let’s assume the diameter is approximately 2.5 inches. Now, assess the internal space of the school bus. Assume a rectangular prism shape for simplicity, with dimensions like 30 feet(360 inches) in length, 8 feet(96 inches) in width, and 8 feet(96 inches) in height.

3. Round-off the numbers to simplify problem: Feel free to round-off numbers to simplify calculation. Always remember that the goal is not to provide an exact answer but to demonstrate a logical and structured approach to the estimation process.

For the above problem, we can follow the below steps to arrive at estimated number:

Calculate the Volume of the School Bus:

  • Volume = Length × Width × Height
  • Volume = 360 inches × 96 inches × 96 inches = 3,317,760 cubic inches ~ 3 Million cubic inches

Calculate the Volume of a Tennis Ball:

  • Assuming a tennis ball is roughly spherical, the volume formula for a sphere is (4/3)πr³, where r is the radius.
  • Diameter of a tennis ball = 2.5 inches, so the radius (r) is 1.25 inches.
  • Volume of a tennis ball = (4/3)π(1.25 inches)³ ≈ 8.18 cubic inches

Estimate the Total Number of Tennis Balls:

  • Total Number of Tennis Balls = Volume of School Bus / Volume of a Tennis Ball
  • Total Number of Tennis Balls ≈ 3,317,760 cubic inches / 8.18 cubic inches ≈ 405,169 tennis balls ~ 400K tennis balls

Nice, so we arrived at estimation of 400K tennis balls total number of tennis balls in a school bus.

You can use any other approach to arrive at a different number. And that’s absolutely fine as long as you specify your thought process and assumptions.

Please feel free to comment below if you used any other approach.

4. Remember common key figures: While there isn’t a fixed set of “essential” guesstimate numbers to remember, having a few key figures in mind can be helpful when tackling estimation problems during interviews. Keep in mind that these are general approximations, and the specific context of the guesstimate question may require adjustments. Here are some useful numbers to consider:

  • Population of the World:
    • Approximately 7.9 billion (as of the last available data)~ 8B.
  • Average Lifespan:
    • Globally, it’s approximately 72.6 years (World Bank data). You can approximate it to 70 or 80 to simplify the calculations.
  • Days in a Year:
    • 365 days in a non-leap year.
  • Hours in a Day:
    • 24 hours.
  • Minutes in an Hour:
    • 60 minutes.
  • Seconds in a Minute:
    • 60 seconds.
  • Average Speed of a Car on Highways:
    • Roughly 60 miles per hour.
  • Speed of Sound:
    • Approximately 1,125 feet per second (or 343 meters per second).
  • Speed of Light:
    • Approximately 186,282 miles per second (or 299,792 kilometers per second).
  • Area of a Football Field:
    • American football field: Roughly 57,600 square feet (including both end zones).
  • Height of a Door:
    • Standard door height: Approximately 6 feet 8 inches (80 inches).
  • Volume of a Basketball:
    • A standard basketball has a volume of about 464 cubic inches.
  • Height of Mount Everest:
    • The highest peak on Earth is approximately 29,032 feet (8,848 meters) above sea level.
  • Length of a Marathon:
    • A standard marathon is 26.2 miles (42.195 kilometers).
  • Volume of a Swimming Pool:
    • An average swimming pool can range from 20,000 to 30,000 gallons.
  • Average Size of a Smartphone Screen:
    • Common sizes range from 5 to 6 inches diagonally.

Also try to remember the numbers related to your country/ region like population, area, etc. For example if you are from India then you can remember below numbers:

Population of India: Approximately 1.44 billion (as of the last available data) ~ 1.4B.

Area of India: Around 3.29 million square kilometers ~ 3.3M sq. km.

Population of Mumbai/ Bangalore ~ 10M (assumption)

You can also ask interviewer if you are not sure of the assumption or estimated number.

5. Remember essential conversion factors: In guesstimate scenarios, conversion factors play a crucial role in converting one unit to another.

Most essential conversion factor: 1 Billion (B) = 1000M & 1 Million (M)=1000K & 1K=1000

Guesstimate Questions
Photo by Magda Ehlers on

Here are some other conversion factors that can be useful in a variety of estimation situations:

  • Length:
    • 1 inch = 2.54 centimeters
    • 1 foot = 0.3048 meters
    • 1 mile = 1.60934 kilometers
  • Area:
    • 1 square meter = 10,000 square centimeters
    • 1 acre = 4,046.86 square meters
  • Volume:
    • 1 liter = 1,000 cubic centimeters
    • 1 gallon (US) = 3,785.41 cubic centimeters
    • 1 cubic meter = 1,000,000 cubic centimeters
  • Weight/Mass:
    • 1 kilogram = 1,000 grams
    • 1 pound = 453.592 grams
    • 1 tonne = 1,000 kilograms
  • Time:
    • 1 minute = 60 seconds
    • 1 hour = 60 minutes
    • 1 day = 24 hours
    • 1 year (average) = 365.25 days
  • Speed:
    • 1 kilometer per hour (kph) ≈ 0.2778 meters per second (mps)
    • 1 mile per hour (mph) ≈ 0.44704 meters per second
  • Temperature:
    • Fahrenheit to Celsius: °�=(°�−32)×59°C=(°F−32)×95​
    • Celsius to Fahrenheit: °�=(°�×95)+32°F=(°C×59​)+32
  • Density:
    • 1 gram per cubic centimeter = 1,000 kilograms per cubic meter
  • Currency:
    • Exchange rates for currency conversion are essential for estimating costs in different currencies.
  • Energy:
    • 1 Joule = 0.000278 kilowatt-hours (kWh)
  • Fuel Efficiency:
    • 1 mile per gallon (mpg) ≈ 0.425 kilometers per liter (kpl)
  • Population Density:
    • Population per square kilometer or square mile, depending on the context.

These conversion factors are valuable for transforming quantities from one unit to another, allowing for more convenient estimations in guesstimate scenarios.

6. Rough estimates based on demographics:

You may also need to take some rough estimats while solving guesstimate questions! Here are some common rough estimates asked in various guesstimate scenarios:

  • Age Distribution: You could estimate that around 25-30% of the population is below 18 years old, 60-65% falls between 18 and 65, and 5-10% is 65 and above. Take number which simplify your calculations.
  • Internet Usage: Globally, you might estimate that approximately 60-70% of the population has regular access to the internet.
  • Literacy Rate: A common estimate for global literacy rate is around 85-90%.
  • Language Proficiency: Assuming English proficiency, you might estimate that 25-30% of the world’s population is proficient in English to some extent.
  • Rural/Urban Population Split: Globally, you might estimate around 30-40% rural and 60-70% urban.
  • Male/Female Ratio: Typically, you might estimate a close to 50-50 split between males and females in most populations.

These are general estimates and can vary based on specific regions or contexts. It’s important to carefully verify these figures based on your knowledge of the specific scenario or location.

7. Communicate Your Approach to the Interviewer: Guesstimate questions not only test your analytical skills but also your ability to communicate your thought process. Its very important to articulate your assumptions and approach in a clear and concise manner before calculating the numbers.

8. Practice Makes Perfect: You can start with solving common guesstimate questions online. Let me know in the comments if you need mock Guesstimate scenarios or practice questions.

Regular consistency and practice will help you become better with solving new guesstimate questions. I would recommend to solve at least 1 guesstimate question daily in order to master this skill.

By combining these points, you can now approach guesstimate questions during your interviews. Never forget that the goal is not to arrive at a perfect answer but to showcase your problem-solving and logical reasoning skills.

At last, I would say that your success in interviews is not a question mark; it’s a certainty waiting to unfold. Believe in your abilities, and let’s embark on this transformative journey together.

You can refer these blogs for other interview preparations: SQL ,Numpy & Pandas.

Hope it helps 🙂

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