Useful knowledge for tech interviews

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World population: 7.3B (July 2015)

Number of cell phones in the world: 6.8B (2013)

Number of Internet users in the world: 3.2B (2015)

Number of cars in the world: 1.2B (2014)

Most populous countries in the world (July 2015):
– 1st China 1.36B
– 2nd India 1.25B
– 3rd US 321M (14% 65+, 23% 18-)

Most Internet users by country (2014):
– 1st China 642M (46% penetration. 22% of world Internet users)
– 2nd US 280M (87% penetration. 10% of world Internet users)
– 3rd India 243M (19% penetration. 8% of world Internet users)

Most popular websites worldwide (2015):
– 1st Google
– 2nd Facebook
– 3rd YouTube
– 4th Baidu
– 5th Yahoo
– 6th Wikipedia
– 7th Amazon
– 8th Twitter

Most popular mobile apps in the US (2014):
– Facebook 115.4M unique visitors age 18+
– YouTube 83.4M
– Google Play 72.2M
– Google Search 70.2M
– Pandora 69M
– Google Maps 64.5M
– Gmail 60.3M
– Instagram 46.6M
– iTunes/iCould 40.5M
– Facebook Messenger 39.2M
– Twitter 34.7M
– Snapchat 26.5M
– Pinterest 24.6M
– Skype 18.8M
– Shazam 18.4M

Most cellphones by country (2014):
– 1st China 1.28B (93% penetration with 47% smartphone penetration)
– 2nd India 960M (78% penetration with 17% smartphone penetration)
– 3rd US 327M (103% penetration with 56% smartphone penetration)

Most motor vehicles per capita by country (2011):
– 1st San Marino 1263
– 4th US 809
– n-th China 113
– m-th India 118
* per capita = per 1000 people

Earth’s surface area:
196.9 million sq miles (510.1 million sq km)
71% covered by water

U.S. area: 3.8M sq miles

Largest states by area (sq miles):
– 1st: AK 665K total (14% water)
– 2nd: TX 270K (3% water)
– 3rd: CA 164K (5% water, 33% forest)
– 18th: WA 71K (7% water, 50% forest)

Cities by area (sq miles):
– 12th: Los Angeles, CA 500 total, 6% water
– 113th: Seattle, WA 140 total, 40% water
– n-th: San Francisco, 232 total, 80% water

Average home size: 1k sq ft (3.6e-5 sq mi)
Average commercial building size: ranging from 10k-100k sq ft from 1920 – 2014, median around 50k sq ft

Number of commercial buildings: 5.6 million (2012)

Most populous states in the US (2014):
– 1st: CA 39M
– 2nd: TX 27M
– 3rd: FL 20M
– 4th: NY 20M
– 13th: WA 7M

Most populous city in the US (July 2014):
– 1st NYC 8.5M
– 2nd LA 3.9M
– 3rd Chicago 2.7M
– 10th San Jose 1M
– 13th SF 852K
– 20th Seattle 668K
– 29th Las Vegas 614K

Median household income in the US: $53K (2014)

Most profitable industries (2014):
– 1st Health $21.8 billion
– 2nd IT services $19.3B
– 3rd Business products and services 18B
– 4th Energy $17.5B
– 5th Financial services $17.2B
– 6th Human resources $12.3B
– 7th Logistics and transportation $11.1B
– 8th Consumer products and services $10.7B
– 9th Construction $10.3B
– 10th Telecommunications $9.4B

World’s largest tech companies by revenue (2014):
– Apple $183B (55% iPhone, 18% iPad, 13% Mac, 9% iTurnes/Apps)
– Amazon $89B (37% AWS, 26% merchandise, 4% media)
– Microsoft $87B (33% Office, 26% Azure, 24% Windows, 13% Skype/Xbox)
– Google $66B (62% adWords, 21% adSense, 9% other, 8% Motorola)

Unemployment rate by state (2015):
– WA 5.3
– NY 5.5
– CA 6.3

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