Do you have trouble understanding the question? Or have trouble about how to start?  Or do you get an answer that doesn't make sense? 

Anyway, this is geometrical probability, abut length.  The total length of the whole sample space is $50$.  The desired intervals consist of numbers within 2 units of a multiple of $10$, thus we want $(8,12)$, $(18, 22)$, etc.  Remember though, $0$ and $50$ are also multiples of $10$ and the interval near them are $(0,2)$ and $(48,50)$.  Now the probability is just the total length of these intervals divided by $50$.