This is referred to as mental maths where most calculations are done in your head. This is fun, as you do not need to go through a lot of trouble to get solutions to most problems. Some of the methods that you can use to practice and learn this field are:
Memorizing time tables- this is one of the oldest methods to learn mental maths. This has worked well over the years as it has been used by many students. It helps one to make simple multiplication problems. Although it is an effective process it has limitations especially when one is dealing with big numbers. This is because most tables deal with two digit numbers thus one cannot be able to multiply numbers that have three digits or more. This is a disadvantage especially in some countries like India, where students are discouraged from using gadgets like calculators in the exam rooms.
One of the formal methods of learning maths is by using Abacus mental maths. This method traces its roots to Asia. This teaches students to practice basic calculations like subtraction, division addition and multiplication. Here you are able to deal with big numbers where you can perform calculations on long and large numbers. You can also be able to come up with square roots and squares of some problems. The latter however depends on the division or multiplication. This is taught using old century tools known as Abacus.
Another method used is known as verdict mental maths tricks. This method traces its roots to Southern Asia. Teachers use old scriptures that were used in India to teach the subject. No tools are used to teach the subject. This is a more advanced mode of learning as you not only learn the simple calculations but you also learn complex maths like geometry, statistics and algebra. This helps one to solve complex and advanced problems with ease. This should be taught at an early age so that the children can use them in future without any problem. This is where you can find a student finishing their maths exam within a very short time and getting good grades.