Question

The sum of the digits of a two digit number is 5. On reversing the digits of the, it exceeds the original number, by 9 . Find the origina number .

Answer 1

let  be the tens digit =x
let  be the units/ones digit =y
the sum of the digits of a two digit number is 5 , so 
 x+y=5
when the digits are reversed, the number is 9 more than the original 
since x is your tens digit, its value is  10x
so you have the value of your original number 10x+y 
Now when u reverse the digits the number = 10y+x
so the equation formed = 10y+x = (10x+y)+9
10y-y=10x-x+9
9y=9x+9
9(y-x)=9
y-x=1
y+x=5
2y=6
y=3
y-x=1
therefore
3-x=1
-x=-2
x=2
therefore the original number is 23