Since we need to find out largest possible remainder which can be obtained by taking largest one digit number which is 9 . now we find any five digit number say 99998 , we cannot take 99999 because its divisible by 9 and gives remainder 0 .
therefore dividing 99998 by 9 gives remainder 8 which is largest remainder obtained by dividing by 9 .
The 60$ system had a greater percentage decrease because it was a lower number to begin with. Taking the same portion out of two different numbers will always be a greater decrease for the lower number.
