There are 50 people in a block of flats, all staying at home because of COVID-19. To pass the time they spend a lot of time using Social Media to keep in touch with friends and family.
36 people use Facebook
35 people use Twitter
40 people use Instagram
42 people use Snapchat
What is the minimum number of people who use all four forms of Social Media?
The total number of Social Media application uses is 36 + 35 + 40 + 42 which is 153. If all 50 people use three forms of Social Media that makes 150 application uses. This leaves three unaccounted for, and so at least three people must use all four applications.