MathDB

Two people write a

2k

-digit number, using only the numbers

1, 2, 3, 4

and

5

. The first number on the left is written by the first of them, the second - the second, the third - the first, etc. Can the second one achieve this so that the resulting number is divisible by

9

, if the first seeks to interfere with it? Consider the cases

k = 10

and

k = 15

Problem Statement