Question

the sum of a two digit no. and the no. obtained by interchanging its digits ,is always a multiple of ...........

Answer 1

The answer is 11.

Proof : Let the one place digit of a number is y and that of ten is x.

So, number = 10x + y.

When it will be reversed then new number = 10y + x.

Now,

Sum of these numbers

= 10x + y + 10y + x

= 11x + 11y

= 11 ( x + y ).

Therefore the answer is 11.