Hi Roy867.
To get to Q50, you have to strengthen your weaker areas of quant and improve accuracy.
To determine which areas to strengthen, consider things such as which types of quant questions you'd rather not see on the GMAT, which ones take you the longest to answer, and which ones you haven't worked on as much as others.
Then work on each area by first reviewing the concepts and making sure you get them from the ground up and then doing dozens of questions in that area until you practically can't miss them.
To improve accuracy, make accuracy a priority. In other words, you know plenty about how to go about answering quant questions. Now, focus on learning how to be accurate and consistent, because being accurate takes a certain set of skills that you can develop.
One way to improve accuracy is to use the Streaks method. In other words, do practice questions untimed and shoot for streaks of 31 quant questions correct in a row. The idea is to learn what it takes to get 31 quant questions correct in a row so that, when you take the GMAT, you'll know not only how to go about answering questions but how to get them correct close to 100 percent of the time
For more on improving accuracy, see this post.
Improving Your Accuracy on the GMAT