You: What's the score? Did I miss much?
Me: It's 2-1 for elAhli and the second half just started. The first half was quite boring.
You: Who scored first? elAhli or ezZamalek?
Me: What difference does it make?
You: Big difference! I can predict the outcome of the match if I knew the order of which goals were scored in the first half.
Me: What do you mean?
You: It's 2-1 for elAhli, right? One of three things could have happened: elAhli scored two goals then ezZamalek scored; Or, elAhli scored its first goal, then ezZamalek, then elAhli again; Or, ezZamalek scored first, then elAhli scored its two goals.
Me: So?!! I still don't understand what difference does that make? It's still 2-1 for elAhli! Why don't you just relax and let us continue watching the game in peace.
You: You don't understand!! I believe the probability of who'll win depends on the order of how goals were scored. Now I have to predict the outcome for 3 possibilities.
Me: And what if the score was 3-2? What would you have done then?
You: I would have to work for 5 different possibilities. No?
Me: Of course not! The number of possibilities isn't always equal to the sum.
You: Can you tell me when will it be equal to the sum?
Me: You're a programmer, why don't you write a program that counts the number of possibilities and compare it to the sum?
You: I don't have the time, I want to watch the match. Besides, I have nine other problems to worry about.
Me: I'll give you a hint. The possibilities will be equal to the sum only if one of the teams scored a certain number of goals.