Question

the sum of digits of a two digit number is 7.if the number formed by reversing its digit is less than the original number by 9 find original number

Answer 1

Let the digits be X and y
According to the question,
X+y = 7 --------- equation 1

9-10x + y = 10y+X
-11x - 9y = -9 ------- equation 2

Now,u can solve the two equations by any method like graphical, elimination,cross multiplication or substitution method

Answer 2

two didit no is represented as 10x+y
given :x+y=7.............eqn 1
no formed by reversing digits is 10y+x
given:10y+x=10x+y-9
       so10y-y+9=10x-x
           9y+9=9x
          9(y+1)=9(x)
dividing both sides by 9
               y+1=x
therefore x-y=1................eqn 2
adding eqn 1 and 2 
             2x=8
             x=4
 substituting x in eqn 2
             x-y=1
             4-y=1
             y=4-1
              y=3