তিন অংকের বৃহত্তম ও ক্ষুদ্রতম সংখ্যার পার্থক্য কত?

Let the number be 10X + Y, (Y is in unit place and X is in the tenth place) 

So the sum of the digits will be X + Y if the sum of the digits subtracted from the number than the result will be 10X + Y - (X + Y) = 9X

So the number resulting will be always the product of 9 so if its need to have 6 in unit place

So the value of X must be 4 as e result it will be $9 \times 4 = 36$ here 6 in the unit place so all the two digit number which has 4 in tenth places will be the number

 So total such number will be 10 (40, 41, 42, 43, 44, 45, 46, 47, 48, 49) (ans.)

The maximum number of Tk. 10 notes is 6.