Most of the people try to memorize the steps and formulas for solving the aptitude questions. Its totally wrong. Each and every aptitude questions are the real world problems. You should forget that you are in an interview and should think commonly to solve the given questions. And I recommend you to answer the simple questions first rather than trying to solve the more complicated questions. If you pickup the more difficult question it will consume more time and may lead to many unanswered questions at last. And you should always keep an eye on the time, because if you select simple questions at first there may chance of completing the test with unanswered questions. The reason is, the companies which recruit the employees will expect quick response time and fast problem solving skills from the employees, so all the questions will be prepared in the way that can be solved within the given time.

     If your time is going to complete and there are lots of questions remaining means, don't get nervous and try to find the option that matches at least approximately to the given question. And try to answer all the questions within the given time. The online test platforms of the companies are mostly designed with a feature to make the candidate easily identify the unanswered questions by marking those question numbers in different color (say Red) or putting them in the different columns like unanswered questions.