One of the underrated, but key skills, in taking the GMAT, is the ability to quickly convert between fractions and decimals. As time is of the essence when working on a GMAT math problem, deciding if it is faster to solve a problem using decimals or fractions can make the difference between completing every question and running out of time.
When approaching a problem in which you will have to work with non-integers, you should always make an active decision whether decimals or fractions will allow you to get to the answer more quickly. In order to do this effectively on test day, you should practice solving both ways while studying. Exactly which problems will be faster using fractions, and which using decimals, will be different for everybody, so it is key that you determine the types of problems in which you find each more efficient.
Additionally, you should learn common decimal and fraction equivalencies. You must learn what 1/2, 1/3, etc., all the way to 1/11 equal as decimals, as these show up repeatedly on the GMAT. Additionally, if you know 1/8 = .125, you can quickly determine that 3/8 equals .375 by multiplying by 3.
If you encounter a fraction for which you do not know the decimal equivalent, your best move is to convert it to a fraction that has a denominator of 100 or 1000. Then just drop the denominator and put the decimal point in the appropriate place.
By using these strategies you will be able to work through problems featuring non-integers more quickly. This in turn will give you more time for other problems and, ultimately, lead to a higher score. For more on this topic, see our Kaplan GMAT Video on Fractions & Decimals.