Even as a degree-less person who is currently teaching himself computer science and mathematics, I realize the problems starts between the fourth and the fifth equal sign in the 'ans' section. If you independently do the calculations at the fourth step, you get 0/0. Interestingly, the same miraculously changes to 20/10 at the fifth step i.e (10+10)/10. The trick seems to have been diving (10-10) by itself and falsely giving 1 as the answer rather than the infinity it is supposed to be. After all, (10-10) is 0 which divided by 0 becomes infinity. Therefore, the conclusion cannot be correct. Anyway, someone seems to have cleverly played with mathematics, here.