Question
A number consists of two digits. The sum of the digits
is 7. If 9 is subtracted from the number, its digits are interchanged. Find the number.Solution
Let the ten’s digit be x. Then, unit digit = 7- x . No.= 10x + (7-x ) = 9x + 7 No. obtained by reversing the digits = 10(7- x ) + x = 70-9x (9x + 7) - 9 = 70- 9x , or, 9x + 9x = 70 - 7 + 9, or, 18x = 72 or x = 4, so ten’s digit = 4 and unit digit = 3 Hence, the required number = 43.
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