What is the Chance of Poker Flush $5/52$ ?
I think the answer should be $$\frac{C_4^1C_{13}^5}{C_{52}^5}.$$
But the writer of my textbook said the answer is $$\frac{C_4^1C_{13}^5-C_4^1-C_4^1C_9^1}{C^5_{52}}.$$
I am confused. Hoping someone can help me. Thanks in advance!