The assessment will consist of a multiple choice questionnaire based upon your personality and working experiences, there are no real right or wrong answer. Just answer them which you feel best reflect your working attributes.
As illustrated by Michael.Y the calculations are very much as mention in the above. Your allowed to use a calculator, but each question is timed along with a timed period in which to answer.
Each test will probably be conducted online. I've recently passed these assessments for a position as a customer host then progressed through the whole recruitment process to land a position as a Customer Host.
Don't be fooled by the practice questions, they'll just be an indication in which the equations will be displayed on the screen. There bear no reflection on the difficulty of the real eqautions you'll be asked on the actual assessment.