then u need to do calculations everyday to know where u r lacking behind.
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practice makes a man perfect ! do maths everyday atleast 1 hour a day
Well I too was weak in calculations, but as I practiced everyday regularly for one month, I noticed a change in my speed of calculating, and I could understand the solutions questions by just seeing them, once these very question were too difficult for me. You can follow the method of setting a stopwatch for 1 hour and try to solve the toughest questions, and gradually your speed and understanding of calculations will increase.