I just did a Windows Anytime Upgrade from Home to Ultimate. Which to my surprise was very quick and smooth. Anyways, I want to install Windows XP Mode to help with answering questions related to Windows XP on Super User and other Stack Exchange sites. 

Before I download the 500MB file from Microsoft's site, I want to know if it prompts for a serial number? If it does, do I need to buy a Windows XP license? If doesn't require a new license but still require a serial number, do I use the Windows 7 Anytime Update from Home to Ultimate key?


Question: Probability exercise with apples
Answer: Hint:  she has to pick 2 red and 7 green, then pick a red. How many ways are there to do that?  How many ways to pick 10 apples?

Added:  to pick an unordered 2 red and 7 green, you need to choose 2 out of 10 red and choose 7 of 90 green. Divide this by an unordered choice of 9 of 100