jmc

This is equivalent to asking for the probability that at least one of the numbers is a multiple of $5$, since if one of the numbers is a multiple of $5$, then the product with it and another integer is also a multiple of $5$, and if a number is a multiple of $5$, then since $5$ is prime, one of the factors must also have a factor of $5$, and $5$ is the only multiple of $5$ on a die, so one of the numbers rolled must be a $5$. To find the probability of rolling at least one $5$, we can find the probability of not rolling a $5$ and subtract that from $1$, since you either roll a $5$ or not roll a $5$. The probability of not rolling a $5$ on either dice is $\left(\frac{5}{6}\right)\left(\frac{5}{6}\right)=\frac{25}{36}$. Therefore, the probability of rolling at least one five, and thus rolling two numbers whose product is a multiple of $5$, is $1-\frac{25}{36}=\frac{11}{36},\boxed{\frac{11}{36}}$