Buy a test preparation book and complete it. The math on the problem solving section of the test will cover basic arithmetic, geometry and algebra. These high school math topics will be included in your exam prep book.
Join a class. Enroll in an online or in-person GMAT review class. Your local university can help you find one that will fit your schedule.
Practice. There are many online sites and books with GMAT problem solving practice questions; keep practicing until you are very comfortable with these basic math skills.
Read carefully. Statistically, 60 percent of math errors are actually reading errors. Make sure that you understand what the question is asking before you answer it.
Use your scrap paper. Work out every question with your pencil and paper. Often, seeing the work, will allow you to catch mistakes that would otherwise cost you points on the exam.
Work backwards. The GMAT problem solving section is a multiple choice exam. It is perfectly acceptable to start with the answers given and find which is the correct solution to the problem.
Guesstimate. Time is of the essence when you are completing the GMAT problem solving section. Simplifying the questions by rounding percents, fractions and decimals to amounts that are easy to manipulate will save you time and energy on the exam.