Regarding your timing issues, honestly, the best way to improve your timing is by improving your GMAT quant skills. As you develop mastery of each individual quant topic, better timing WILL follow. In fact, a great way to know how well you have mastered a particular topic is to be cognizant of your reaction time when seeing a particular question. For example, consider the following simple question with which many students who are beginning their prep struggle:
14! is equal to which of the following?
(A) 87,178,291,200
(B) 88,180,293,207
(C) 89,181,294,209
(D) 90,000,000,003
(E) 91,114,114,114
Upon seeing this question, what is the first thing that comes to mind? Trying to add up the values in the expression? If you are able to quickly recognize that using the “5 x 2 pair rule” will allow you to attack the problem quickly and efficiently (see the solution below).
Solution:
14! = 14 × 13 × 12 × 11 × 10 × 9 × 8 × 7 × 6 × 5 × 4 × 3 × 2 × 1.
Notice that there is at least one (5 × 2) pair contained in the product of these numbers. It follows that the units digit must be a zero. The only number with zero as the units digit is 87,178,291,200.
Answer: A
Although this is just one example of many, you see that you must have many tools in your toolbox to efficiently attack each GMAT quant question that comes your way. As you gain these skills, you will get faster.
Lastly, you may find it helpful to read the following articles about
The Phases of Preparing for the GMAT and
Timing Strategies For a Higher GMAT Quant Score.
Good luck!