GMAT PS: You will never need to do heavy calculation
One of the reasons why the GMAT is my favourite test of all is that it is so well defined in terms of the skills tested and consistently so. One of the things that is absolutely essential to remember on the GMAT Problem Solving (PS) is that the test-setters do not want you to do donkey work with respect to calculation. The leading companies in the world are not paying thousands of dollars to hire graduates from premier b-schools to do what a calculator can do!