EGG BOILING PUZZLE ANSWER

Answer = 9 minutes

Here is how to do it:

Time	Action	Time remaining before action		Time remaining after action
		4 Minute	7 Minute	4 Minute	7 Minute
0	Turn over both hourglasses	0	0	4	7
4	Turn over 4 minute hourglass	0	3	4	3
7	Turn over 7 minute hourglass	1	0	1	7
8	Turn over 7 minute hourglass	0	6	0	1
9	Take egg off stove	0	0	0	0

 

Thanks to The Grey Labyrinth