Another simple one:
You have two fuse wires and you know that the fuse wires are known to burn at various speeds along its own length. However you do know for certain that each fuse will burn out in an hour exact.
With no other equipment besides a lighter, how do you measure 45 minutes?
Folding wouldn't actually work too well, since each of the 1/4 segments would still be burning at various speeds, some will burn out faster and others slower, which means they won't burn out at the right time.
You are thinking along the right lines though.
Assuming you only need to measure 45 minutes and can be present the whole time (rather than needing to light and leave) then the following should work...
light both ends of one fuse, and at the same time light one end of the second fuse. The fuse with both ends lit will be completely burnt in 30 minutes, at this point light the other end of the second fuse which will then take a further 15 minutes to burn out completely.
that wouldn't work. The 1st fuse would burn in 30min but the 2nd fuse would have ROUGHLY 30 min left due the varying speed at which it burns
Bill Door has it right as far as I can tell