mathematics tricks and fun

 Maths Tricks and Fun 15-digital-sum Hello friends today we will study how multiplication becomes easy by the use of digital sum .What is  digital sum? It is the sum of the digits of a number  . Here its use in multiplication of big same digit  numbers ,their squaring and cubing are discussed.  Here use of digital sum in squaring of 4digit number  is shown the digit is 4 ie (4444) are to be squared..so  first we multiply the two outer fours 4×4 is 16 . We will write 1 then a gap and 6.Digital sum of 16 is 7 . So we have totally 8 digits in the answer.and outer digits we  have written and three digits each from either side we have to fillup.For this we will add 7 from either side  and progress Arithmetically . so 1+7 is 8,8+7 is15,  15+7is 22 stop here we have finished 4 digits on this  side .we will add 7 to the other side. 6+7 is 13, 13+7  is 20, 20+7 is 27. Now will add the carry overs and we  get 197...