Hi, I thought you may like this Mentalrobics exercise from Braingle.com:
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Icebreaker: Number Actions

Icebreakers [ For more on 'Icebreakers ' go here: http://www.braingle.com/mind/226.html ] are little exercises that help relax tension and loosen up a formal atmosphere in a meeting where you want to have creative ideas and group participation.

At your next meeting, write the following rules up where everyone can see them:

1. Divisible by 3 = raise/lower left hand
2. Divisible by 4 = raise/lower right hand
3. Divisible by 5 = stand up / sit down

Now, recite all the numbers from 1 to 100 and have everyone perform the required actions. See how many people have it correct in the end. You should be sitting with both hands up in the air.
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For more mind exercises: http://www.braingle.com/mind/