Hi Cazca,
thanks for the added information about the time it takes to process calculations. This is very common in our calculator-dependent world. In fact everyone always has one handy now given that cell phones have built-in calculators. The more we are dependent on these, the slower the calculations seem to come on their own.
As a first step, I would recommend relearning the multiplication table you knew when you were in elementary school. The standard 12x12 grid with the perfect squares along the main diagonals. I've seen students struggle with math like 7x8 and 3x7 and 9x12 which take a couple of seconds at most when you know them off-hand. It also comes in handy for all kinds of problems that require factoring or divisions. For example, consider questions such as:
425 + N is divisible by 7. If N is between 0 and 7, what is N?
If you don't know the multiplication table, you might take 30-60 seconds to try and figure out how many times to multiply 7 to get close to this number. However, if you know that 7x6 is 42, then you quickly realize that 7x60 is 420, and you don't have to slog through the calculations at all! You drop 420, are left with 5, and correctly deduce the answer is N=2.
There are other important mathematical concepts to memorize, such as common fractions (from 1/2 to 1/10) and things, but nothing gives you higher Return On Investment than knowing your multiplication tables forwards and backwards. (Note: Please don't learn them Backwards a la Toys Я Us, forwards will be sufficient!)
_________________
Ron Awad
Veritas Prep | GMAT Instructor
Save $100 on Veritas Prep GMAT Courses and Admissions Consulting Services
Veritas Prep Reviews