Hi desertEagle.
The quant questions on Manhattan practice tests are known to often take longer to answer than actual GMAT questions. So, to a degree, what you experienced was due to the nature of the questions on the test you took. At the same time, you may still want to speed up in GMAT quant. So, here are some ideas.
One thing you can do is learn things that you'll often need so that you have them at your fingertips when you need them. Some of these things are the following:
- Learn to prime factor all the numbers from 1 to 200 in your head so that you can quickly find the prime factors of any number.
- Learn fraction to decimal conversions for all sixths and sixteens.
- Learn the square roots of 2 and three.
- Learn the common Pythagorean triples.
Another thing you can do is answer practice questions in more than one way each, seeking to determine which way is the fastest for that type of question.
Also, you can seek to reduce careless errors because careless errors can slow you down by forcing you to redo questions. For some tips on how to reduce careless errors, see this post.
Improving Your Accuracy on the GMAT