If I roll two dice, what is the probability that the two numbers rolled add up to $8$? Show assumed knowledge

The probability is the number of ‘favourable’ outcomes (the number of ways the dice can add to $8$) divided by the total number of outcomes.

There are $6\times6 = 36$ total outcomes. Of these, $5$ of them add up to $8$: $2+6$, $3+5$, $4+4$, $5+3$, and $6+2$. If you’re confused about why both $2+6$ and $6+2$ are counted, see Question 14.1.1. The probability is $5/36$.