Depends how intelligent you are, or rather how good your memory is as it really is only a memory test. For the multi-choice part of the test you have to answer 43 out of 50 questions correctly. The...
£37
$48 (additional $10 to retake written test; additional $20 to retake driving test)
NO! You must pass your theory test before you are even allowed to take the practical driving test.
For cars, it's 43/50 for multiple choice, 44 out of 75 for hazard perception - you must pass both