Probability to not change bouquet

[svyessayan]

Q: MGMAT Num Prop Guide 5th Edition - page 121, #5

A florist has 2 azaleas, 3 buttercups, and 4 petuninas. She puts two flowers together at random in a bouquet. However, the customer calls and says that she does not want two of the same flower. What is the probability that the florist does not have to change the bouquet?

The book shows us literally listing each possibilty. Is there a formula where you do not have to list? Overall, I just do not understand the explanation. I only got to 9! / 2! 7!.

[tim]

I believe your question has been answered quite thoroughly in the other posts on this topic. Please let me know if I'm wrong about this.

guide-4-word-translations-chapter-5-problem-10-t9344.html

word-translations-probability-chapter5-t6493.html