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. combinatoricsnumber theorydivisibledividesDigits