Hi, I thought you may like this Mentalrobics exercise from Braingle.com:
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Engineering Challenge : Paper Tower

Engineering challenges are fun activities that are frequently assigned to students in physics or engineering classes, but they can easily be used outside of these venues. An engineering challenge usually has a simple goal and some rules about what sorts of materials you are allowed to use. These are great ways to get people thinking creatively and to foster teamwork and competition. Try an engineering challenge at a birthday party, office outing, scout meeting, or any other gathering where you want to have fun and exercise your creativity.

The objective in the Paper Tower challenge is to construct the tallest freestanding tower from a single sheet of paper and a small amount of tape. The tower must be able to stand on its own for at least 10 seconds.
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For more mind exercises: http://www.braingle.com/mind/