I wouldn't take any individual practice test result too seriously, unless you're doing the GMATPrep tests
. It's extremely difficult for GMAT test-prep companies to accurately reverse-engineer the GMAT, and none of them are able to perfectly reproduce the scoring system. So take Knewton
's test result with a grain of salt. It's certainly possible to miss a bunch of questions and still get a 51, but 12 missed questions (or maybe 10, since there are only 37 questions on the quant, and not 39...?) seems awfully high for a 51.
More importantly, it probably isn't a great idea to focus exclusively on quant, unless your verbal is unbelievably good. You can't really cram for verbal, especially the CR and RC questions, so if you need improvement in that area, you'll probably need consistent practice over a long period of time. While I can't take the 51 completely at face value, it's clear that you have some pretty solid quant skills, and you want to make sure that your studies are at least somewhat balanced between quant and verbal.
I hope this helps! Good luck with your studies.
Helping students kick the GMAT in the nuts since 2002... www.gmatninja.com.