Using only a four-minute hourglass and a seven-minute hourglass, measure exactly nine minutes–without the process taking longer than nine minutes.
Bonus made-up Question: Can you come up with a generalized solution of the hour glass problem?
This is a more involved version of the "Die Hard III Problem: A classic water bottle riddle. How to produce exactly 4 gallons with a 3 and a 5 gallon pan" whose solution can be found here
Assume that equal amount of sand slipped down measures equal intervals of time, i.e. amount of sand slipped to measure the first minute is same as the last minute.
Solution posted by Gold and Iron (Nikhil Pandey, CSE IITB 2009 Alumnus), Mohit Johari (Civil IITB 2011 Alumnus) , Nikhil Simha R (Amazon India SDE, CSE IITB 2012 Alumnus) and Sravan Kumar (EE IITB Final Year Student) in comments!