Plato,
No calculators, they want to check out your mental arithmatic. Besides, these are the kind of questions you should really be able to do faster in your head than by the time you've got the calculator out of the drawer, keyed in all the numbers etc.
If I recall correctly there were about 25 questions, but it was a while ago now. If you have a look back in the thread around the beginning of September you should be able to find a post I put up after stage 1 which goes into more detail.