wow, that sucks majorly.
well., i hadnt heard that about drama, but id say for most things, youd be right to generalise and say 50%. i imagine the only subjects where there would be a difference would be in subjects that you have to submit work to an external marker, like ext2 eng, art etc. however, you should have been provided with dates for all of your internal and external exams and their weighting by the faculties at your school at the start of the year. if you missed out on that, go see your teacher and ask: it's a mandatory requirement. they, or the head teacher, should be able to answer any of your questions, its their job to know those things.