Question 279490
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Here is a quick mental solution you can use if formal algebra is not required, and if the speed of finding the solution is important -- as in a timed competitive exam.<br>
The difference between a 2-digit number and the number with the digits reversed is 9 times the difference of the two digits.  Since the difference between the two 2-digit numbers is 36, the difference between the two digits is 36/9 = 4.<br>
So the sum of the two digits is 12 and the difference is 4.  Quick mental reasoning shows the digits are 4 and 8.<br>
So the original number is 48 and the number with the digits reversed is 84.<br>
ANSWER: 48<br>