How many trees are there on your college campus?

At first, this type of case interview question may appear difficult and even unpleasant, but after you know what actions to do, they will become a lot more pleasurable.

I'll walk you through each stage, offer you some pointers, and give you some practice problems. It won't be long before you can answer all of their market-sizing and estimate questions!

What are Guesstimate Questions?

In interviews, candidates are asked to estimate a figure based on very limited information (thus the term "guess"). It takes a combination of mental math, logical thinking, problem-solving skills, and background knowledge to answer these questions correctly.


  • How many tennis balls can fit inside a Boeing 747?
  • How many trees are there on your college campus?
  • How many bottles of beer are there in Bangalore right now?
  • How many weddings are being performed in India at the moment?
  • How many litres of white paint does it take to paint the Parliament?

How to Answer Guesstimate Questions?

These steps can help to answer guesstimate questions:

  1. Clarify any terminology in the question that is unclear.
  2. Divide the total into 3-5 little, easy-to-estimate chunks.
  3. Calculate the value of each item using math and prior knowledge.
  4. To get to the final outcome, combine the components.

Even if you have the correct figures, don't jump to a conclusion. It's all in the strategy, you must be really regimented and top-down at all times!

Clarify the problem

Make sure you and the interviewer are on the same page about every detail of the question.

Clarifying the situation at the start serves four purposes:
  • It provides you with the information you need to solve a situation that is otherwise unclear.
  • It brings you and the interviewer on the same page, avoiding future conflicts.
  • It demonstrates an ideal, systematic problem-solving method, comparable to what consultants perform.
  • It affords you some time to consider the issue.
Because guess estimate questions are virtually always confusing about critical facts, you should never skip this phase. If it appears apparent to you, you're missing those ambiguous areas.

Break down the problem

Request a timeout, then divide the task down into manageable chunks to estimate.

Each tiny item must be easier to estimate than the large portion; if you can't estimate the small bits, you're either not breaking down the task well enough, or you're doing it incorrectly.

Solve piece by piece

This is where you solve each puzzle component on your own.

Do not attempt this during the "timeout" phase; it will most likely turn the otherwise brief timeout into a protracted awkward silence, which is undesirable.

Add all the pieces

Consolidate the elements into a final answer using calculations.

This phase requires quick mental calculation; if your math is too slow, you will bore the interviewer to death. However, don't rush it; incorrect calculations are a no-no in case interviews.

Practice your mental math and fine-tune it for consulting case interviews.

Guesstimate Questions – Tips and Tricks

1. Ask close-ended clarification questions - Limit the alternatives to only those that are beneficial to you when clarifying. Close-ended questions (or even affirmatives) assist impose favourable definitions, easing your guesstimating procedure — most interviewers are unsure of the facts, so they're open to your ideas. Open-ended inquiries, on the other hand, pass over authority to the interviewer, making the question far less predictable.

2. Make defendable, fact-based estimations - To make your estimates more defendable, base them on facts and reasoning. After all, consulting is a fact-based profession, and being accountable is the desired quality. As a result, the interviewer is likely to ask you about your estimates, so be prepared to defend them.

3. Round up the numbers for easy calculations - Round the numbers to make math easy on your brain. Ideally, you should alternate between rounding up and down such that the offsets cancel each other out and your margin of error is as small as possible.

4. Perform regular sanity checks - Check your figures on a regular basis to ensure that they are correct — logically, factually, and mathematically. It's easy to make mistakes with all the complicated data, estimations, and the tough process of breaking down the problem.

5. Solve the problem with explicit visual aids - Draw the problem trees and point to them as you speak. It's easy for both you and the interviewer to get lost in a maze of facts and estimates if you don't have such visual aids. Furthermore, if you don't sketch out your issue tree, you'll appear disorganised, which isn't acceptable in a case interview. On a side note, tables can help you visualise your solutions. Tables are substantially more compact than issue trees, making them ideal for solving difficult problems.

Common data

Although the data for market-sizing and estimate issues isn't always predictable, two sorts of data do appear frequently:
  • Population
  • Factors affecting demographics (life expectancy, age structure, income segments, education, etc.)
Those two data kinds frequently exist on three scales on a geographical basis:
  • Your own neighbourhood (country/region)
  • Countries and regions of importance
  • World
Have fun solving guess estimates questions.