That's not sample rate, that's bit rate.
A sample is one discrete piece of sound. You string thousands of them together over a second, and suddenly you have an approximation of a continuous waveform. That's what digital audio is!
An MP3 is a compressed digital audio file. You take your original digital audio and you throw out everything that MP3 thinks isn't important, and voila, you've reduced your file size by 1000%! Now, of course the "throw away what MP3 thinks isn't important" is a big deal! Hence the higher the bitrate (number of bits used per second of audio) of an MP3, the better quality of the MP3, because it is throwing less away.
An MP3 will have the same sample rate output as the input file had, unless you specificy differently (or it automatically reduces sample rate at lower bitrates).
Slackmaster 2000
