A number consist of two digits whose sum is 10. If 54 is added to the number, the order of the digits will be reversed. What is the number?\n\nLet me see.\n\nLet the ones digit of a two-digit number be x and tens digits to be y. Then the sum of the number is x+10y.\n\nReversing the digits we get y + 10x.\n\n54 + x + 10y = y + 10x\n\n54 + 10y = 10x - x\n\n54 + 10y = 9x\n\n54 = 8x - 10y\n\nOur two systems of equations are \n\nx + y = 10\n8x - 10y = 54\n\nCorrect system? The answer is 28.