Question
The sum of the digits of a two-digit number is 9, and
when the digits are reversed, the number decreases by 45. Find the changed number.Solution
Let unit digit be x and ten's digit be y. Original number = x+10y Reversing the digits, new number = 10x+y 
Also, x + y = 9(eq2) Add eq1 and eq2 = 2x = 4, or x = 2 Substitute in eq2 = 2 + y = 9, or y = 7 Hence, Original number = 72
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