Sorry to hear about your score. You should look here before deciding on a retake: should-i-retake-gmat-thread-retaking-gmat-strategies-83339.html?fl=menu
I would say that for any top 15 school a 660 will put you at a disadvantage b/c you are going to be in the lower range of the 80% range for all of those schools. This means that you will have to be very special in other areas.
Also, with a Q40, your quant skills are going to be called into question. So unless you have other areas of your application (work, college, etc...) to prove that you can handle the quant heavy corriculum, Adcoms are going to question your quant abilities. Your verbal is quite good.
I suggest a retake with a very heavy focus on quant study. I would go back through the Manhattan quant books, and go back to the basics.. Make sure that you understand the fundementals before you start building on tougher areas. Make sure to do lots of practice to reinforce new topics, and use an error log
to keep track of your mistakes. You can do this! With a littl bit of study, you really aren't far away from the 700 at all! Also, quant is considered much easier to learn than verbal. So your battle won't be quite as tough as someone in a reversed situation.
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