Let two digit number that Shiwani thought be '$xy$', where $x$ and $y$ are single digit number.
Therefore, $10x+y=p(x+y)+3$, where $p$ is a natural number
Possible values of $x$ and $y$ for which $p$ is a natural number are:
There are 14 such two digit numbers that give a remainder of 3 when divided by the sum of the digits.
Probability that Devesh thought of the same number as Shiwani = 1/14