when you reverse the digits in a certain 2 digit number you decrease its value by 81 what is the number if you sum of its digits is 9?

90

Step-by-step explanation:

The multiples of 9, when adding the digits of the multiple together, will always produce the number 9. In this case, 81, or 8 + 1 = 9. Since the problem says the sum of the digits is 9, then we are looking for a two-digit multiple of 9. Using the next multiple, 90, we see that 9 + 0 = 9 and if we reverse the digits to 09, we see that 90 - 9 = 81, which is a decrease in value of 81.