Two ordinary six-sided dice are rolled. What is the probability that the two numbers add up to 9?

1. Probability is the size of the event set divided by the size of the sample space. 2. Each die shows one of six numbers, so two dice give 6 times 6, which is 36 pairs. 3. Now list the pairs that add up to 9. 4. They are 3 and 6, 4 and 5, 5 and 4, and 6 and 3. 5. The order of the two dice matters here, so 3 and 6 is counted separately from 6 and 3. 6. That gives 4 outcomes in the event set out of 36 in the sample space. 7. So the probability is 4 in 36. 8. Answering 3 in 36 treats 4 and 5 as the same outcome as 5 and 4, and so loses a pair. _Source: Siyavula Mathematics Grade 11 (Everything Maths, CC BY 4.0), Chapter 10: Probability_