Doing practice problems blindly (without a study plan) is not very useful.
Many of your mistakes are not "silly". The question writers try to make certain answer choices appealing in both verbal and math.
Remember, the test is designed to separate test takers and stratify into percentiles. To overcome this and score higher:
Use your GMATPrep test to figure out what your weakest sections are and WHY (the why part is more important than the what) it is your weakest section
Find material (not questions, material) that will help you overcome these subtopics. Use our book review threads and debriefs to select content
Keep an
error log when you do practice problems and if you are making the same "silly" mistakes, they're not so silly. You're gravitating to incorrect answer choices for a reason. Figure out that reason and work to overcome it.