<p>That depends on the size of the class. Given the fact that a single B will drop you from #1 to #30, I assume your class has over 500 students in it. If that's the case, you will be ok. And of course, it depends what your academic goals are. If you want to apply to MIT or Caltech and your B was in Math or Physics, you can pretty much kiss your chances bye-bye! But if your B was in basketweaving or History, you will probably be fine.</p>