sum of two digit no.is 9 and 9 times no is twice of the no. obtained by inversing the digit.

Let x be the units palce digit and y be the tens palce digit of the number

Given:Sum of two digit no.is 9   so x+y =9  ----(i)

Also, 9 times no is twice of the no. obtained by inversing the digit.

9(10y+x) = 2 (10x+y)

 x-8y = 0    ......(ii)

Solving (i) and (ii)

y =1 and x = 8
Therefore the no. is 18 .