I think it's safe to say at least 3/4 will not do any work. Another 3/4 of the remaining will drop out after trying, and another 3/4 will not understand a thing

I think it's safe to say at least 3/4 will not do any work. Another 3/4 of the remaining will drop out after trying, and another 3/4 will not understand a thing. 900 is still a decently large university class.