Math score is much easier to improve than the verbal score imo.
10 days is pushing it but nevertheless
- read math drill section in OG10, page 32 and on, there they explain the math definitions. It is important to remember them not to make silly mistakes in math
- do several math challenges on http://www.gmatclub.com/. They are much harder than real GMAT but they helped me a lot. They cover lots of important math topics.
- Kaplan math section is very good (in Kaplan GMAT 800 and Kaplan 2005)
- find your weak areas in math and focus on them (solving and understanding 10 problems in each area is enough I think)
main tested ares are - sets, interest, speed/distance problems, rate problems, number properties (primes, odds, evens, remainders), geometry, probs/combinations/permutations, sequences, absolute values and inequalities.
some formula I found useful
combination nCm = n!/(n-m)!m!
permutations nPm = n!/(n-m)!
sums
consecutive integers from n to N, their sum is 0.5N(2n + N -1)
even numbers can be represented as 2k
and odds as 2k+1
numbers not divisible by 3, for example, 3k+1
the maximum number of divisors an integer x may have will not exceed 2*sqrt(x) -1
stuff like that