What do these mongodb errors mean? How to fix it?

Question

linux

I am new to linux. In general, I get used to it for a couple of days. Today I tried to install mongodb following this tutorial and it seems to work, everything works.
However, when I do it in the terminal, sudo apt-get updateI get the following errors

W: The repository 'http://repo.mongodb.org/apt/ubuntu serena/mongodb-org/3.0 Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
E: Failed to fetch http://repo.mongodb.org/apt/ubuntu/dists/serena/mongodb-org/3.0/multiverse/binary-i386/Packages  404  Not Found
E: Some index files failed to download. They have been ignored, or old ones used instead.

The Update Manager in the tray yells 'Could not refresh a list of updates'. When I press Refresh, it gives me
Could not download all repository indexes
The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise, the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct.
The repository ' repo.mongodb.org/apt/ubuntu serena/mongodb-org/3.0 Release' does not have a Release file.Data from such a repository can't be authenticated and is therefore potentially dangerous to use.See apt-secure (8) manpage for repository creation and user configuration details.Failed to fetchrepo.mongodb.org/apt/ubuntu/dists/serena/mongodb-o... 404 Not FoundSome index files failed to download. They have been ignored, or old ones used instead.
What do I need to do to get rid of these messages so that the update manager can automatically refresh?

Answer 1

There are no 32-bit packages per se in this repository. Hence the error. Can not be fixed therefore - https://docs.mongodb.com/manual/tutorial/install-m...

Answer 2

well, what to do? someone help...