Vi For Smarties

Your friend comes to you with an odd request. All she wants you to do is make a simple text file containing the word hello. She asks that you name the file hello.txt. How would you do this using Vi? (Remember to save and quit.)
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Bad move. Now your friend knows you can use Vi, and she wants you to make a longer text file named dummy.txt which contains the sentence "Vi is for dummies." once per line for 23 lines. What is the most efficient way to do this with Vi?
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Your annoying friend is back. She has seen how efficient Vi is, and now wants you to replace all occurrences of the word dummies with the word Smarties in the file dummy.txt. What is the quickest way to do this in Vi?
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She's sulking because her own editor seems useless now. Unfortunately, you've wasted so much time showing off that you've forgotten you have a report to finish. You've also forgotten to wear your watch today, and you need to make this very important deadline. Quickly, how do you access the system's correct time via the Unix date command without leaving Vi?
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Until you have mastered everything on this page, you are not ready for Lesson Five.