Question

How many 2 digit whole numbers are increased by 18 when they're digits are reversed

Answer 1

This can be calculated easily.

As any two digit number can be written in the following form:

N= 10x +y

If we reverse the number now, it would become:

N' = 10y + x

So if we subtract one from the other, we should obtain 18 ( as mentioned in the question ).

N-N'= 18

=> x-y = 2

Thus, any number whose digits differ by two would be an aswer to the question.

The only numbers which satisfy this are : 13,24,35,46,57,68,79

But this would not be true for any 3 or more digit number.