How many windows are in New York? How much revenue does YouTube generate per year?

Use this technique to answer estimation questions from large companies such as Google, Facebook and Amazon.

MANGA (Meta, Amazon, Netflix, Google and Apple) companies are widely recognized as top organizations to work in the world, but they are also recognized because of the challenging that their hiring processes can be.

Apart from the behavioral type questions, one way to assess candidates' problem-solving skills is through estimation questions, also known as guesstimate questions.

These questions can be very diverse, usually giving the impression of not making any sense about the company or the product itself. However, none of these questions has a correct answer; their purpose is to demonstrate our analytical and critical thinking skills when solving them.

What are these types of questions like?

Here are some examples from real interviews of candidates who left feedback on Glassdoor:

• Estimate the number of mobile applications downloaded in Mexico per day.

• Estimate the number of microwaves sold in a week worldwide.

• What is the size of the autonomous car market in 2025?

• What is the storage capacity required to store all Google Street View images?

• What is the required internet speed for a school?

• How many kindergarten teachers are there in the United States?

• What is the weight of a school bus?

Sounds off, doesn't it? What does knowing the weight of a school bus have to do with working at a tech company? 🤔 But here's the secret: There is no right answer. It's a relief that these "trick" questions are not focused on knowing what the real outcome is but evaluating how we solve it.

The wrong way to solve estimation questions

Remember that in an interview, we are being evaluated on our problem-solving ability, not on how quickly we do it. Rushing through an answer can make us look bad to the interviewer and give the impression that we are not sufficiently prepared.

Also, it’s valid to ask the interviewer for time to think about how to solve the problem. We should also speak out loud while proceeding with the resolution, as this will indicate to the interviewer what our thinking is like and also demonstrate that we can communicate procedures and results. Yet let’s try not to consume the whole time looking for an answer.

How to solve an estimation question?

With the following steps, it will be easier to approach an appropriate answer for this type of question.

1. Ask clarification questions

2. Create a solving procedure

3. Add approximate numbers and estimate

4. Review and iterate estimates

Let's see a real example!

Solving an estimation question

How many phone cases are sold in the United States per year?

Step 1: Ask clarifying questions

Clarifying questions will help us better understand the type of answer the recruiter expects. However, we should not stop at this step alone, as the interviewer may think that we just want to get the answer out of him by asking question after question.

Some questions we could ask to shorten the result:

• In this exercise, are we considering iPhone or Android cases specifically?

• Are we focusing only on a specific screen size?

Asking clarifying questions not only points us in the right direction to solve the problem, it also buys us time. While our conscious part of the brain is asking these questions, our subconscious is already figuring out the next step.

Step 2: Create a resolution formula

Now that we have an idea of what the result should be, it is time to create the process to get to that number. For this, we must do small calculations with formulas multiplying percentages. These percentages will be mostly guesses.

As we can see in the graph, we see the steps listed from A to G. The latter being the result we want to reach.

For this, we seek to calculate the following:

• Calculate the number of people with cell phones (letter C).

• Calculate the number of people with cases (letter E)

• Calculate the number of people with cases on their cell phone (letter G)

A highly recommended tip before adding numbers, is to explain step by step to our interviewer how we will proceed to solve the exercise. This can be very useful since the recruiter can tell us if we are on the right track or not.

Step 3: Add approximate numbers and calculate

This step is essential, because here we are going to define numbers based on assumptions. No one expects us to know the exact number of inhabitants in a certain country. Having an approximate value will be more than enough. In fact, in most cases, the interviewer is the one who will suggest making assumptions.

And what assumptions can we make? As many as necessary. Let's take the example graph again.

• (A) The exact population of the United States is 331.9 million. However, for more practical and convenient purposes, it is always best to round the figure so we will leave it at 330 million. Remember that we have limited time in an interview, we don't want to waste time with tenths.

• (B) Assuming that smartphone penetration in the U.S. market is 70% since we are discounting older adults and infants who are still too young to have a cell phone.

• (C) To calculate then the number of people who own a cell phone in the U.S.A. we simply multiply A * B and round the result:

C=A*B=330M*.70=230M

• (D) Then assuming that the percentage of people who use a case for their cell phone is 75% taking into account the following: maybe teenagers and young people do not take as much care of their cell phone as an adult, some cell phones are more resistant than others and not all of them need extra protection.

• (E) To calculate the number of people who have a case, we simply multiply C * D and round the result:

E=C*D=230M*.75=170M

• (F) Finally, considering that buying a cell phone case is not a recurrent expense, let's give it a value of 50%. Here we are saying that of the people who did buy a case, they only bought it once.

• (G) Now, to calculate the last result of people who have a case on their cell phone, we multiply E * F and round the result:

G=E*F=170M*.50=85M

✋ Stop! Although it seems like a good idea to end the exercise here, we still have one last step to go.

Step 4: Review and iterate the estimates

Before we tell the interviewer that we are done and show him or her the final result, we should iterate our assumptions. Why? Let's remember that the assumptions are not absolute. They served us throughout the exercise to arrive at a number, but as a good Product Manager or product manager, it does not mean that our first result is correct.

This demonstrates to the recruiter that we are not married to our bias, and we are always looking for continuous improvement.

What are the areas where we can improve?

• (B) We had assumed that older adults and children were outside the cell phone population. But perhaps this is not entirely true, as there are more and more children with cell phones from an early age and more older adults who want to stay connected to their families through a smartphone. We could increase our percentage based on these new deductions to 80% and recalculate.

• (D) Here we said that not everyone has a case for their cell phone because of the issue of protecting the hardware but, rethinking it better, maybe there are more people with a case on their cell phone because of fashion or aesthetics. There may be young people who have more variety of cases depending on the occasion.

• (F) Following the same line of buying cases for aesthetics, therefore our percentage of purchases per year would also increase. Considering that a person can buy more than one case per year every time a new color or model is released. We modify the percentage and recalculate.

🎉🎉🎉 ¡Congrats! 🎉🎉🎉

Now that we have finished, we move on to share the new result with the interviewer. Not only have we demonstrated that we can solve this type of problem, but we are also willing to challenge the information to arrive at the most optimal result.

The best part is that these exercises can be practiced at home and the same formula applies to almost any estimation question.

Learn other great frameworks from PM Diego Granados