Steam Beta update public key error - Ubuntu 12.04 LTS 64 bit

[TheDrifter363]

Hello, I'm having this unknown issue. When I type in "sudo apt-get update" towards the end, I receive this error: "W: GPG error: http://repo.steampowered.com precise InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F24AEA9FB05498B7". I do not know where to find to key so I may add it so steam can be trusted. This is preventing me from updating steam through the ubuntu update manager. Any help would be appreciated. Btw here are my specs:

OS: Ubuntu 12.04 LTS 64 bit
Graphics: EVGA Gtx 670 FTW+ 4 gb VRAM
Drivers: Nvidia 310.14 beta
CPU: Intel core i5 3570k @ 3.4 ghz
Ram: 8 gb DDR3 @ 1600 Mhz
Storage: 256 ssd crucial m4
Case: Silverstone SG08
PSU: 600 Watt Silverstone 80+ Bronze

[Essence of Concrete]

Do you have this entry in your sources.list file?
deb http://repo.steampowered.com/steam precise steam

[TheDrifter363]

I did not have that entry, thank you for that. However now I have a new error. Most likely because I have a 64 bit ubuntu. Here it is: Err http://repo.steampowered.com precise/steam amd64 Packages
404 Not Found
W: Failed to fetch http://repo.steampowered.com/steam/dists/precise/steam/binary-amd64/Packages 404 Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.

Anyone know of any workaround?

[TheDrifter363]

*bump*

[AlamA]

the line should be:
deb [arch=i386] http://repo.steampowered.com/steam/ precise steam