Vedic Mathematics for Competitions: Addition, Subtraction, Multiplication, Division, Squaring, Cubing, Square- root, Cube- root (Tricks in Mathematics Book 2)

This is the second part in this series. You might have found several books in the market covering the basic calculation tricks from the Vedic mental mathematics. But the most basic techniques could not be found anywhere. Well...what is mental mathematics and can someone really learn is the question. Let me answer this question first of all. Mental math has to be performed in your mind and without using pen or paper. Yes, it is possible to learn to do it. Let me tell you how.
When you go to a vegetable vendor the vendor calculates the total amount to be charged and then returns you the balance. They usually don't use computer or calculator. So, they perform the addition and subtraction mentally. You can also do it. Suppose you had to add 78, 36, 42 and 49. First steps would be to turn them into numbers that we can easily deal with. 78 could be turned into 80 or 70 based on whether you would like to perform subtraction or addition later. Let's say we wanted to subtract later, then 78= 80-2, 36= 40-4, 42 is 50-8 and 49=50-1. Now, 80+40+50+50=220. Also, add the negative numbers now, so we get -15. So 220-15 is off course 205.
There's one more trick where you could keep the positive and negative numbers together, based on whether they were closer to their prior 10s multiple or later. It would be wiser to take 42 as 40+2 than taking it as 50-8. Look at what happens when we do that. 78=80-2, 36=30+6, 42=40+2, 49=50-1. Now 80+30+40+50=200, and -2+6+2-1=5. Therefore, again by applying the technique it comes out to be 5.