If you plan on having a career in the consulting industry, you need to know how to guesstimate. Guestimation can feel like a daunting task, especially when you first look at the kind of questions asked. From the market sizes of large conglomerates to revenues and populations, calculating some of these quantities even close to a ballpark is realistically impossible.
However, it is here that you must realise that guesstimation is never about the answer. Guesstimate interview questions assess you according to the approach that you take in solving a certain question. This approach tells your prospective employer whether you are fit for the job you are applying for.
Guesstimates are generally asked in the first round of consulting company interviews. Typically, this will be followed by a business case round and then a personal interview. Guesstimates require significant amounts of practice before you sit for the interview. The use of a pen and paper in the guesstimation round will be permitted. Still, the aim must be to solve the question in such a way that the interviewer can understand your approach, regardless of whether the calculations were correct or not.
Key Points About Answering Guesstimation Questions
- No correct answers: No guesstimate question has a correct answer. No guesstimate question also has a correct approach. When you start solving a guesstimate question, your aim must not be to reach a correct answer or apply a correct approach. If the question you have been asked seems realistic—such as the market size of a particular good—do not believe that you will be able to reach the correct answer or anywhere close to it through guesstimating.
The aim must be to be logical. The approach you take toward solving the question, and every step you take after the previous, must follow and seem to lead toward a correct answer. Additionally, do remember that it is highly unlikely that the interviewer knows the correct answer either. You are being assessed purely based on how you are tackling the issue.
- Don’t tie yourself up in knots: Scores of students and interviewees, in the endeavour to reach as close to a correct or realistic answer as possible, will end up assuming such quantities that can take minutes to calculate. Calculating 0.75% of 2.5 million can be hard in a crunch situation, with an interviewer assessing your every move and awaiting your next step. This is yet another reason why you must not look for correct answers.
The interviewer has likely provided a question without numbers—if you end up confusing yourself or having too many difficult numbers to calculate, it is probably your fault. Make sure always to round up or down when approaching guesstimate questions. Rounding up or down makes remembering numbers and calculating them very easily and can help you proceed to the next step much faster.
- Write it down: You will likely be given a pen and a paper when you appear for the guesstimate round. If you aren’t and believe that the question asked will require one, you can ask for writing material. While you are solving the question, make sure to write every part down. If your question ever requires segmentation, make a flowchart showing the different segments you have created and conduct each segment’s calculation under the respective segment subhead.
Do not treat the piece of paper as a rough calculation sheet. The interviewer may eventually ask for this sheet and mark you down if your working seems illegible. What you write and how you write it are both essential parts of the question you are answering and can prospectively help you solve the question in a much better manner.
- Speak up: Writing while speaking, and indeed vice versa, can be a challenging task. However, make sure that you are clearly and directly communicating your approach to the interviewer. Again, the interviewer is not looking for your answer; it is the approach that is being assessed. Do not treat the guesstimate question as a mathematical query; instead, consider it a logical one and focus on communicating the reasons you opt for each step to the interviewer.
An excellent method of avoiding writing while speaking can be to first inform the interviewer clearly of the next step and then move on to the quick calculation. Do not spend too much time on the calculation. The time you speak for should always be greater than the time you spend calculating.
Steps For Solving a Guesstimate Question
- Step 1: Before jumping into the calculation, you must make all essential clarifications in the question itself. There is no limit to the kind of questions you can ask the interviewer. In general, try not to ask questions leading directly to an answer and stay away from questions whose answers might be numerical. Instead, try and stick to yes-or-no questions that it is easier for your interviewer to provide answers to.
However, do make sure that you get all your doubts clarified before you proceed with the calculation. You can ask questions during the solving process, but making the right start is equally important. Asking questions also brings you and the interviewers on a common platform regarding the question prerequisites and allows you some extra time to think about your approach.
- Step 2: Break down the problem into smaller and small pieces through successive steps. Here, you must take no more than about 4-6 steps in reaching your final determination. If you break your problems into smaller pieces, but successive pieces are just not small enough, it will take too much time before you reach close to the metric you are required to calculate.
At times, you will need to segment the problem into two or smaller pieces and then calculate separately for each segment. Make sure that each segment is assigned a proportion that is both logical and easy to calculate. Assigning a percentage share like 27% to a segment will make your calculation impossible, so stick either too simple fractions or tens of percentage points
- Step 3: Only after you have determined your approach must you start solving. Do not begin solving before you have determined how you are going to reach your final answer. It communicates the wrong message to the interviewer concerning your strategy of tackling problems.
Additionally, once you have decided upon a strategy, it becomes easier to assign proportions that are calculable. Also, do not calculate in silence. Keep speaking and guiding the interviewer through your process, and ask any necessary questions. You may even stop to ask if your approach is logical.
- Step 4: This is the final step of the guesstimate solving process when you reach the answer. Recheck your calculation and examine if any calculation seems off. Do not pay heed to how much the individual answers match a possible realistic answer in your mind. Add up all the individual pieces of the guesstimate and report a final answer.
Guesstimate Interview Questions and Answers Examples
1. How many cups of tea were consumed in Mumbai last month?
First, clarify the question. Then, start solving.
As a first step, inform the interviewers that each day of the week is being considered equally. Tea consumption might likely decrease during the weekend as people do not go to the office—so you might consider that as well. We shall go with the first assumption.
The population of Mumbai is 18 crore; we shall round it up to 2 crores. 20% of this population is assumed to be children who do not drink tea. Another assumption is that of the remaining population, 20% are habitual drinkers, 30% are regular drinkers, 20% are occasional drinkers, and 10% are non-drinkers.
The habitual drinkers may be said to have three cups of tea in a day. Regular drinkers may be said to have one cup of tea in a day. The tea consumption of occasion drinkers maybe once a week, and that of non-drinkers none at all.
Habitual – 3 x 0.2 x 7 = 4.2
Regular – 1 x 0.3 x 7 = 2.1
Occasional – 1 x 0.2 x 1 = 0.2
Non – 0
Total = 6.5
Total cups per week = 6.5 x 1.6 crore = 10.4 crore
2. How many iPhones are currently being used in India?
Clarify with the interviewers whether the question is about only a single version of the iPhone or all versions put together. Here, we shall assume that all iPhones put together are being talked about.
The first step toward solving this query will be segmentation. There are many ways in which India’s population can be segmented. Here, we shall first assume that only people who have attained a working age and are under the age of retirement own an iPhone. Children and old citizens do not own an iPhone. This removes 20% of the population as children and 20% as senior citizens.
The next assumption will be that only the upper stratum of India’s income range can afford an iPhone. This metric assumes that only 5% of the eligible citizens from the previous filter can own an iPhone.
Now, it is not necessary that every member of this upper stratum will own an iPhone. Other options, such as OnePlus, Samsung, etc., are also available. However, a fair assumption would be that 50% of the eligible population from the previous filter owns an iPhone.
Calculating the proportion of the population that owns an iPhone –
0.6 x 0.05 x 0.5 = 0.015
Total iPhones in India = 0.015 x 130 crore = 1.95 crore
3. How many cars are there in Delhi?
Clarify whether the interviewer assumes just personal vehicles or all cars, as Delhi is also a government seat. The assumption in this solution will be that only personal vehicles are being talked about.
Firstly, the population of Delhi is 2 crores, rounding up. The average size of a family in Delhi may be said to be four people, it being an urban region mostly composed of nuclear families. Further segmentation may be as per income class or level. As is customary, 30% of people may be said to belong to the lower class, 50% to the middle class, and 20% to the upper class.
The calculation metric will be the number of cars per family. Among middle-class families, 50% may be said to own a car, and the other 50% own no car. Among the upper-class families, it may be said that all families own an average of two cars.
Middle class families – 0.5 x 0.5 x 1 = 0.25
Upper class families – 0.2 x 2 = 0.4
Total = 0.65
Total cars in Delhi = 2 crore * 0.65/4 = 32.5 lakhs.
4. What is the size of the laptop market in the USA?
Make important clarifications such as the unit of measurement. Here, we shall assume that the unit of measurement is the number of laptops sold in a year.
The first step will be to make clear the USA’s population, which may be taken to be 300 million. Next, assume the proportion of this population that owns a laptop. The last determination will be the average span of the life of a laptop in the USA.
The USA population may be segmented into retirees, students, stay-at-home population, and working population. The working population may be said to be 50% of the total population. The retirees maybe 30% and students maybe 20% of the whole population.
Among the working population, it is assumed everyone owns a laptop. Among the retirees, a fair assumption would be that nobody owns a laptop. Among students, while younger classes do not require laptops, older classes do. So, half the students may be assumed to own a laptop.
Calculating the proportions of the population that own a laptop –
Working population – 0.5 x 1 = 0.5
Students – 0.2 x 0.5 x 1 = 0.1
Total – 0.6.
The average age of a laptop may be said to be 5 years. So, ⅕ of the total calculated population will change their laptops every year.
The market size of laptops in the USA is 350 million x 0.6 x 0.2 = 42 million.
5. How many ping-pong balls can fit inside a Boeing 747?
Begin by asking the interviewer the size of a ping pong ball. If you do not get an answer, assume a value.
To calculate the number of ping pong balls that fit inside a Boeing 747, we can begin by calculating the volume of a Boeing 747. First, assume the total number of seats on the plane. Then, account for the extra space—the aisles, the galleys, and the washrooms.
The additional space will be the space in the overhead compartments and the space above the passenger’s head. Now, divide the volume that you have calculated by the volume of the ping pong balls that you have assumed. Do not forget to account for the empty space between the balls.
Let’s say there are 400 seats in a plane. If we consider the aisle to occupy one seat’s space, and there are 40 rows with two aisles, that adds 80 more seats. Let us say the area above the seat is about the same as the seat itself. That makes 960 seats in total. The washrooms and galley might add space worth about 20 more seats, making the total count roughly 1000 seats.
Each seat can be said to occupy the amount of volume a human takes up in the sitting position. Assuming this to be 4 ft x 2 ft x 1 ft, the total seat area is 8 ft. Hence, the plane’s total volume becomes 8000 cubic ft or 13824000 cubics in. Let us say the area occupied by a ball is 4 cubic inches. The total number of balls hence becomes 3456000. Considering that balls can be packed only with about 70% efficiency, the total number of balls becomes 2419000.
The above guesstimate interview questions and answers will give you a firm insight into what guesstimates are and how to solve them. However, do always remember that the best way to solve guesstimate interview questions is by practice and practice alone.
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