Remember that in order to learn how to quickly solve the examples written or in the mind, you need to practice constantly. Buy collections of mathematics examples and solve daily two or three dozen. Take your time and go directly to next topic, if not refresh your memory of the previous one. If examples are not enough, stack, subtract, multiply and divide the first numbers. Even if it's the numbers of the adjacent cars in the Parking lot near the house.
Be sure to write down at first all his calculations, and then check with the calculator. If you find a bug, will solve this example again in order to find out exactly where you made the error in the calculations.
Constantly repeat the multiplication table. Only when you again with easy to operate single digits, move on to double digits. The easiest way is to divide the multiplicand and the multiplier in the tens and ones. For example, 45×56 = 45×50 + 45×6 = 40×50 + 5×50 + 40×6 + 5×6 = 2520. With sufficient training you will be able to solve these examples , not only in writing but also in mind. Most importantly, do not mix numerals and follow the order of action. The same method use in the construction of two-digit numbers in a square.
To learn how to quickly fold and subtract multi-valued numbers in mind, always focus on the numbers that are multiples of 10, 100, 1000, etc. for Example, if you want to add the 3723 and 675, you won't need to count the first number is "not enough" to "round" - 4000. In this case, 277. Next: 675 – 277 = 398. Thus, we find that the total is 4398. If you want to subtract from 3723 675, calculate a second number of "not enough" to "round" - 700. Ie: 700 - 675 = 25. Subtract the first number 700 and then add 25. The result: 3048.