To be honest, you'll need at least an 80% for it to not be an issue at all. 70% is the absolute minimum.
Also, it depends on what your college major was and the mix of courses you took. If you are a humanities major with little to no quant courses, then you will need an 80%. If you can't get there, then you should enroll in extension classes either online or locally at a community college -- take calculus, stats, algebra or whatever quant-oriented course to show that you're prepared for the quant aspects of b-school. Now, if you were an engineering major in undergrad, then it would still be nice to get an 80% on the quant, but you'll still need a 70% minimum (and if you were an engineering undergrad, you should be able to hit 70% or greater anyhow if you're prepping for the exam properly).
Alex Chu
alex@mbaapply.com
www.mbaapply.com
http://mbaapply.blogspot.com