Maths problem

[lana-54]

Hey everybody,
I cannot work this out and it is really annoying me!
If you have 3 wooden rods that have no markings on them that are equal to the lengths of 11cm, 9cm and 7cm how can you use these rods to measure 1cm?
Am I the only one who can't understand this??

[Joyofsox]

3x7=21
2x11=22
difference is 1cm

poke the 9cm rod in the eye of the questionmaster, you don't need it for anything else.