I have done some work on working this out myself, and have come up with a formaula that gives a rough estiamation of the number of sutdents that acheive a study score of 50. If you did Methods, you can use the Normal Distribution technique to work it out more presicely, but the this formala I have developed workes pretty well.

Students with a 50 SS= (Number of students doing the subject/1000)X2

As an example, If I use 2008 Further Maths and 2008 English as examples, it shows that it is pretty good. I got these statistics from my teachers so blame them if Im very wrong.

FURTHER MATHEMATICS

Students with a 50 SS= (24000/1000)X2

Students with a 50 SS= (24)X2

Students with a 50 SS= 48

The actual Number of students to obtain a study score of 50 was 49 or 50.

ENGLISH

Students with a 50 SS= (44000/1000)X2

Students with a 50 SS= (44)X2

Students with a 50 SS= 88

The actual Number of students to obtain a study score of 50 was about 90-95.

It's not totally accurate, but is is an easy formula to use in your head.