i cant divide big numbers
It's not that you "can't" but rather it's just that you haven't yet learned how to do it. I assume that you are referring to long division.
Since you do not give me a specific example, I searched Google under the key words "long divison" to get these possible sources:
http://www.mathsisfun.com/long_division2.html
http://en.wikipedia.org/wiki/Long_division
http://www.coolmath4kids.com/long-division/long-division-lesson-1.html
http://www.doubledivision.org/
I hope this helps. Thanks for asking.