My provincial exam #2

@Trung Đặng Đoàn Đức – Ừ. Vậy mà cho ng ta cho lớp 6 :v Tớ xem giải trong sách rồi, hay hơn cách của tớ nhỉ? :D

@Vinayak Srivastava – I feel that this method is sufficient to show that 11 is the least difference since the ending digits are cyclic. There was no need to even know the options since there is no other outcome other than 5^y ending in 25 and 36^x ending in 16, 36, 56, 76 or 96. We can see that 36 - 25 is the current minimum, so we just need to check if $(\ldots36 - \ldots 25)$ is possible. And the solution has proven that it isn't possible because then 5^y must be div by 3, which isn't possible except y=0, but y>0