There are $7$ out of $36$ outcomes which are prime numbers under $6$: $1+1$, $1+2$, $1+4$, $2+1$, $2+3$, $3+2$, $4+1$. 
Peter rolls two standard six-sided dice at the same time. What is the probability that the sum of both rolls is a prime number less than $6$? 
1. $\dfrac{7}{36}$. 
2. $\dfrac{1}{6}$. 
3. $\dfrac{5}{36}$. 
4. $\dfrac{1}{9}$. 
5. $\dfrac{5}{12}$. 