School timing

[GmatKiss]

IMO: C

[mathbyvemuri]

stmt(1)=> crux is "4/5 th of total students arrived by 8"
stmt(2)=> crux is "10 students arrived after 8"

So, the conclusion from (1) and (2) is:
1/5 th of total students is 10 => there are 50 students in total. And 50% of that ie., 25 attended by 7AM.
Answer "C"