Quote:
Originally Posted by xpi0t0s View Post
With a stopwatch, obviously.
Oh really, that was quite cunning.

Quote:
Originally Posted by xpi0t0s View Post
Which you'll need anyway, because how else would you know that the 7-minute and 4-minute timers are accurate?
We know that 'cuz he man who sets the questions defines it for us.

You are not expected to use any kind of tricks here like using a stop watch. Simply use the two hourglasses, compare time as nimesh or naimish pointed out and get a measure of 9 min.