Test case 2,3 failing why?

Question

Creating a file with 1 to n numbers with different lines my output was correct but test case 2 , 3 are failing please check it
https://code.sololearn.com/cb991L4Tz16S/?ref=app

Answer 1

Narendhar Kothuri
The ‘a‘ mode writes the file from the end of it and doesn’t care about what has already been written, while the ‘w’ mode erases the file to an empty state and starts writing and the beginning of the file.

Answer 2

Can you please explain me what is exact difference between 'a' and 'w' mode