Exercise 7

1- Design a to do list web application for a product manager.

2- How many golf balls can you fit in a bus?

Post and review answers and feedback to answers in the comments section of this post.

See also:

How to answer an estimation question in a product manager job interview

List of estimation questions for product manager job interviews

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Here is my take on the number of golf balls in a bus.

Let’s assume the volume size of a bus is 8 meters x 2 meters x 2 meters = 32 cube meters. Now, given that there are sets and other things in the bus, we will assume the available space for the golf ball is 80% of the 32 cube meters = 0.8 x 32 = 25.6 cubic meters

Now, if the golf ball was a cube, its volume size (assuming radius is 2 cm) would be 2cmx2cmx2cm = 8cubic centimetre. Now, given that it’s a sphere, let’s assume it’s 10% smaller. or it’s 7 cubic centimetres.

Now, to calculate total number of balls of size 7cubic centimetre in a container of 25.6 cubic meter, I divide 25.6 x1,000,000 cubic centimetres by 7 cubic centimetres.
25.6×1,000,000 / 7 = 3.5×1,000,000 which is 3.5 million.


This is a great example. Thank you. This website is really helpful.


Shouldn’t the diameter of the ball be considered (instead of the radius) while calculating the volume of an equivalent cube?


You’re right. The diameter should be considered. So the volume of the ball would be
4cm x 4cm x4cm = 64 cubic centimeter. So, the total number of balls would be 1/8th of what I have now. 3.5milion / 8 would be around 4400K


When I think about the PM persona, I can think of a few unique things they do:
– they prepare presentations and present their roadmap, status, etc. to the rest of the organization
– they write user stories and requirements
– they might have to create quick mock ups and wireframes
– they work with developers to ensure project is moving forward
– they review and analyze data to help them shape their roadmap
– they hear customer feedback and work with the UX research team

For the sake of this example, I’m going to focus on the use cases that need preparation (e.g. PM has to spend time to prepare a presentation) and therefore, the product manager needs to allocate time to complete them. So, the use cases to focus on with this web to do list app are
– they prepare presentations for the senior managers
– they write user stories and requirements
– they might have to create quick mock ups and wireframes

The to do list app can help PM complete these tasks on-time by helping PM in the following format:

– PM can select the deadline by which he’ll have to complete the task. This feature is standard among many to-do applications.
– PM can select the type of work (presentation, user stories, requirements, create mock ups, other). This is specific to the PM world. The type of the work will be the type of work that a PM generally does.
– The web app suggests a list of mini-tasks associated with the particular main task. For example for creating a presentation, it suggests 5 mini-tasks : prepare data, create draft, present draft for initial feedback, obtain feedback, update presentation according to feedback
– The web app then allows the PM to select the date by which he’d like to complete each mini-task. The can also make recommendations on the completion date of each mini-task based on historical data. Once PM choses the deadlines for each mini task, the web app connects to the PM’s calendar, checks for available timeslots in their calendar, and suggests a few meeting requests that helps the PM block times in his calendar to allocate for working on the mini-tasks. The meeting requests time and length will be suggested based on historical data.
– Once the PM accepts the time and suggested length of the meeting invites, the invites will be sent to the PM. This way, the PM has blocked his time for working on the mini-tasks in the future.