MathDB

In an examination, there are

3600

students sitting in a

60 \times 60

grid, where everyone is facing toward the top of the grid. After the exam, it is discovered that there are

901

students who got infected by COVID-19. Each infected student has a spreading region, which consists of students to the left, to the right, or in the front of them. Student in spreading region of at least two students are considered a close contact. Given that no infected student sat in the spreading region of other infected student, prove that there is at least one close contact.

Problem Statement