Bu there is a better way if you wanna take 52s square you must first 5x5 = 25 add two (00) and then like x you must multiple the sides 5X2 + 2x5 = 20 add one (0) and the last 2x2 = 4 and the answer is 2500+200+4 = 2704
Strap in everyone, here we go: General multiplication of two two digit numbers: 'AB' x 'CD' = (10A + B) x (10C + D) = 100AC + 10AD + 10BC + DB This always works. it is the foil method. The "trick" showed here boils down to: 'AB' x 'CD' = 100 (AC + D) + BD for this trick to work the results of both formula should be the same 100AC + 10AD + 10BC + DB = 100 (AC + D) + BD We can subtract BD from both sides --> 100AC + 10AD + 10BC = 100 (AC + D) expand the brackets on the left hand side --> 100AC + 10AD + 10BC = 100AC + 100D Subtract 100AC from both sides --> 10AD + 10BC = 100D divide by 10 --> AD + BC = 10D This is the prerequisite for this formula to work. In both examples given the unit digits were the same (i.e. B = D) which would simplify the prerequisite to --> (A + C) x D = 10D --> A + C = 10 But it would also work for 28 x 77 = 7x8 + 100x(2x7+7)= 2156