Exercise 3

1- How would you improve the Starbucks app?

2- What is the market size of toilet paper in Canada?

You can submit your answers in the comments section of this blog post to receive feedback. You can also see other people’s answers, the feedback they received, and give your own feedback in the same section.

The article how to answer an estimation question in a product manager job interview helps you prepare for estimation interview questions. And the article how to answer a product improvement question in a product manager job interview helps you prepare for product improvement questions.

Here is a list of estimation questions for product manager job interviews and here is a list of product improvement questions for product manager job interviews.


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1- How would you improve the StarBucks app?
I think one of the problems that StarBucks can solve is enabling one person to order for a few friends and split the bill properly. Currently, if I am going to StarBucks, I rather not ask my colleagues if they’d like me to grab coffee for them because there is no easy way for them to pay me. The solution to this problem would be a ‘split bill’ feature that allows a person to split / share the bill.

To measure the success of this feature, one can look at % who try the functionality and reuse it again. Another business performance metric one can look at is if there will be an increase in the $ value of online orders.
The above feature can help increase revenue per customer per pick up.

2- To measure the market size of toilet papers in Canada, I will need to know the estimated total number of toilet paper rolls sold / used per year in Canada. Given the estimated population of Canada is 30million, I just need to estimate the number of toilet paper rolls used per person.

Let’s assume that on average, each person uses toilet papers twice a day, each time using 20 sheets. So, one person uses 40 sheets per day. For simplicity, I will assume that people of all ages use toilet paper twice a day. Now, since one year has 365 days, an average person uses 365 days x 40 sheets per day / 1000 sheets per roll = 14.6 rolls per year. I will assume that one case of toilet paper is 18 rolls at the price of $10 per case. So, a person uses 14.6 rolls / 18 rolls per case = 0.8 case per year.

This means that 30 million people in Canada use 30 million x 0.8 case per year per person = 24 million cases per year. Since each case is priced at $10, the total sales volume of cases of toilet paper sold is 24 million x $10 = $240 million. If I wanted to do a quick sanity check, I think about how many cases of toilet paper I buy at home. I buy 1 or 2 cars per year. This is alighted with the 0.8 case use per month.

Product Management Exercises

Good answers to both questions. On question 2, I would have tried to come up with a more accurate estimate on the amount of toilet paper used per person. You can highlight that between age range of 0 to 2, there are no uses of toilet paper. And between 3 to 5, the usage of toilet paper is probably half of an average person. Here is how you can do more calculations to calculate the number of sheets used per person per year.

0 – 2 years – 0 sheets per day

2 years to 5 years – 10 sheets each time – assuming there is 2 usages per day in this age group ,the average number of sheets per day for this age group is 2 x 10 sheets = 20 sheets per day

5 years to 80 years – 20 sheets each time – assuming there 2 usages per day in this age group ,the average number of sheets per day for this age group is 2 x 20 sheets = 40 sheets per day

On average, a person uses this many number of sheets per day:
(assume population is distributed equally among the society and people age range is between 0 to 80.)
0 sheets per day x 2 years / 80 years + 20 sheets per day x 3 years / 80 years + 40 sheets per day x 75 years / 80 years =
0 + 0.75 sheets per day + 37.5 sheets per day = 38.25 sheets per day


could you also base this off of the amount of time it takes you to finish a roll of toilet paper?


For question 1, improving starbucks app

I would start by getting to understand the objective of the improvement. Is it to improve revenue or engagement.

Lets say it is to improve revenue. Then looking at the personas who use Starbucks app frequently, I would call out 3 – Busy office folks, Travelers and Coffee Connessiurs

Picking up one of the personas, lets say busy office folks, their customer journey has the following painpoints
1. Finding the store closest to them with min preparation time
2. Easy parking spots
3. Knowing coffee is ready

Focusing on their biggest pain point, i.e.” Finding the store closest to them with min preparation time”, we can start with a few solutions.

1. Display a map of nearby stores with total time to reach+ the time to get the order ready in the selected shop based on traffic data and queue in each store.

2. Automatically choose the best store for the customer depending on total time at each store, giving an option of changing the store if required.

3. Give an option of prioritizing their order in the nearest store by paying higher for the coffee in peak times.

Choosing the best solution based on impact to revenue, ease of implementation and customer wow, I would go with solution 3.


Hi Mac,
Thanks for the answer. I think you follow the structure well and do a good job of listing the persona’s. I would have listed a few more pain points and a few more creative solutions. Also, you will need to explain in more detail how you would evaluate your solutions based on your criteria. Explain how you would evaluate each of them. I like your solution #3 though. It’s very interesting. You’d probably get a bonus point in the interview:) if you also explained how you’d go about implementing solution 3 and how you’d go about testing how it’s performing.


Thanks Bijan for the feedback. I usually stick to 3 points whether on pain points or solutions. Also, I agree that rough implementation plan and measurement would be a good idea to mention