Estimation & Sizing

Question 1

What are the two things that estimation questions usually test for?

Answer 1

• Quantitative skills (e.g., 20M photos * 5MB per photo)
• Product judgment (e.g., “It’s reasonable to assume that users might upload 5 photos for this use case…”)

Question 2

What are the two pillars of “product sense” in the context of an estimation question?

Answer 2

• Make reasonable assumptions
• Ignore the irrelevant

Question 3

List four common types of estimation questions.

Answer 3

• Revenue opportunity (how much could we make with subscription X)?
• Market sizing (what is the TAM for Slack?)
• Storage Needs (how much space do we need for photo storage?)
• User behavior (how many shows are watched per day on Netflix?)

Question 4

What trap do some candidates fall into regarding rounding in estimation questions?

Answer 4

They think that doing math precisely will be impressive and avoid rounding even when it makes sense to do so.

Question 5

What is the world population, approximately?

Answer 5

7.8 billion

Question 6

What is the population of Asia, approximately?

Answer 6

4.7 billion

Question 7

What is the population of Africa, approximately?

Answer 7

1.3 billion

Question 8

What is the population of North America, approximately?

Answer 8

600 million

Question 9

What is the population of the European Union, approximately?

Answer 9

450 million

Question 10

What is the population of South America, approximately?

Answer 10

440 million

Question 11

What is the population of China, approximately?

Answer 11

1.45 billion

Question 12

What is the population of India, approximately?

Answer 12

1.4 billion

Question 13

What is a good estimate for the number of people per household in the US?

Answer 13

Roughly 2.5

Question 14

What is a good estimate for the number of people per household in a less developed county, like El Salvador or Indonesia?

Answer 14

4

Question 15

What is the population of the US, approximately?

Answer 15

330 million

Question 16

What is the population of Indonesia, approximately?

Answer 16

280 million

Question 17

What is the population of Brazil, approximately?

Answer 17

220 million

Question 18

How many daily active users does facebook have?

Answer 18

1.9 billion

Question 19

How many daily active users does Amazon (the consumer site) have?

Answer 19

500 million

Question 20

Approximately how much does cloud storage cost?

Answer 20

In the ballpark of 2 cents per gigabyte per month.

Question 21

Approximately how much storage space is required to store a web-optimized (compressed) JPEG image?

Answer 21

On the order of tens of kilobytes.

Question 22

Approximately how much storage space does audio (e.g. mp3) require, per minute?

Answer 22

Roughly 1 megabyte per minute.

Question 23

Approximately how much storage space does a lossless photo require, per megapixel?

Answer 23

Roughly 1 megabyte per megapixel.

Question 24

Approximately how much storage space does an HD video require, per hour?

Answer 24

Roughly 2.5 Gigabytes per hour.