How can I delete multiple lines in vi?

I find this easier

1. Go VISUAL mode Shift+v
2. Select lines
3. d to delete

https://superuser.com/questions/170795/how-can-i-select-and-delete-lines-of-text-in-vi

You can delete multiple(range) lines if you know the line numbers:

:[start_line_no],[end_line_no]d

Note: d stands for delete

where,
start_line_no is the beginning line no you want to delete and end_line_no is the ending line no you want to delete. The lines between the start and end, including start and end will be deleted.

Eg:

:45,101d

The lines between 45 and 101 including 45 and 101 will be deleted.

Sounds like you're entering the commands in command mode (aka. "Ex mode"). In that context :5d would remove line number 5, nothing else. For 5dd to work as intended -- that is, remove five consequent lines starting at the cursor -- enter it in normal mode and don't prefix the commands with :.