Question 21
Let $n \ge 2$ be a positive integer. A positive real number is written in each unit square of a $2 \times n$ grid, so that the sum of the two numbers in each column is $1$. Suppose that, regardless of the numbers written, we could always delete one number from each column so that the sum of the remaining numbers in each row is at most $a$. What is the smallest possible value of $a$?
(Battsengel B.)
(Battsengel B.)