I'm wondering how many MP3's (on average) should I be able to put on a CD (700 MB) ?

I want to play them on an Alpine car deck that plays MP3's. I have a CD with 212 MP3's that I burned a couple years ago, and the deck plays the disk just fine. But now, when I put say, 100 MP3's, Windows Media Player (for example) wants to break them up into 4 CD's and when I do put them all on one, my deck says error. What am I doing wrong? Shouldn't I be able to put a couple hundred MP3's (with average length songs) onto one CD and play them in my deck?? Very confused.