The sum of two digit number is 9


Asked by admin @ in Math viewed by 327 People


The sum of digits of a two-digit number is 9.Also,nine times this number is twice the number obtained by reversing the order of the digits.Find the number.

Answered by admin @



Let the tens place digit be a

And Unit place digit be b

According to first condition,

a + b = 9 -------(1)

According to second condition,

9 ( 10a + b) = 2 (10b + a)

=> 90a + 9b = 20b + 2a

=> 90a - 2a + 9b - 20b = 0

=> 88a - 11b = 0

=> 8a - b = 0 -------(2)

On adding equation 1 and 2, we get

9a = 9

=> a = 1

On Substituting the value of a in equation 1, we get

1 + b = 9

=> b = 8

Required number = 10 a + b

= 10 × 1 + 8

= 18

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