let the no be (100)x + (10)y + z now x>y>z.

the reversed no. is 100z + 10y + x now subract.

                 

                        100x + 10y + z

                    (-) 100z + 10y + x 

 now if u do normal sub. z-x will be - so what do we do recall from the 1 st standard. borrow.

 

                        100x + 10(y-1) +10+ z

                    (-) 100z + 10y      + x    even now u need to borrow.

 

                        100(x-1)  +100+ 10(y-1) +10+ z

                    (-) 100z       + 10y             + x    now sub.

 

      =            (100( x-1-z)) + (100 -10 )+ (10 +z -x)

               // i have enclosed each digit in  brackets.

      =            (100( x-1-z)) + (10(9) )+ (10 +z -x)   now reverse this no.     

 

                  (100(10 +z -x)) + (10(9) ) + ( x-1-z) now add.

 

     =           (100( x-1-z +10 +z -x) +90 + 90 +(10 +z -x + x-1-z )

     =            100 *9 +180 + 9

     =           1089!!!