That's right. NO CALCULATOR on exam day. In fact, you can't bring anything into the exam room. All pens and plastic transparent sheets will be provided to you by the center.
So, it is time to crack some brain cells when you prepare for Quantitative section. The tricks in solving Quant(itative) questions are (1) to rephrase the question into an mathematical equation, (2) ask yourself what is the "x" they want you to solve, and (3) play the elimination game. Of the 5 answers, eliminate those that you know are wrong. This increases your chances of getting the right one especially when you run out of time.
Remember, you must answer all questions. Leaving any unanswered means heavy (and I do mean heavy) penalty on your final GMAT score!