what percentages are you talking about?
i hope this addresses your question:
some schools use an index number to rank or sort their applicants. the index number is obtained by multiplying your LSAT score by some set number, multiplying your GPA by some other set number, taking some other set constant, and adding them all together. the result is an index number. the formulas (i.e., the three different set numbers) are released by the law schools that use them, and they're on a chart somewhere on LSAC's online services (right underneat where you can see your academic summary report).
what to do with this number: once you know what your number is (either because you plugged in the numbers yourself or because you saw your index number on your LSDAS report to a particular school), it's meaningless until you see what's a good index score for a particular score. (because of the range of multipliers, some schools have high index scores around 3.6, others have high index scores in the 100's.)
take the 75th percentile LSAT and GPA for a school (obtained from USNews or LSAC-ABA official guide to law schools or the school itself), and plug those numbers into their formula. if the resulting index number is lower than your index number, that indicates that you have a very good chance of getting accepted.
do the same thing with the 25th percentile numbers. if your index number is below the resulting index number, your chances of acceptance are very low. if your index score is in between the two index scores you got from 75th and 25th percentiles, you're borderline.
not all schools use index scores. there's more on this, but a lot of it is speculation, as schools don't generally admit to doing anything substantive with their index scores (or at least the schools i've asked, which were all in the top 25).