Hi, I thought you may like this Mentalrobics exercise from Braingle.com:
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Forgetting Speed

Sometimes we forget a fact almost instantaneously and sometimes we can remember it for the rest of our lives. If a fact is stored in our short-term memory [ For more on 'short-term memory' go here: http://www.braingle.com/mind/25.html ], we are more likely to instantaneously forget it again. But once information enters our long-term memory [ For more on 'long-term memory' go here: http://www.braingle.com/mind/113.html ], it still may be in danger of being forgotten. Studies have shown that the rate of forgetting is highest shortly after the learning happens and tapers off as time passes. Additionally, we may remember the general idea much longer than specific facts.

The more thoroughly you learn the subject, the less likely you are to forget it. This is because you are reinforcing the memories more deeply into your mind by overlearning [ For more on 'overlearning' go here: http://www.braingle.com/mind/18.html ] the topic. Information learned quickly will also be forgotten quickly.

Another factor that determines forgetting is the amount of reinforcement that you give these memories. If you learn something and then are never asked to recall that information, it is going to be forgotten much more easily than if you use the learned information on a regular basis. So, if you want to remember something, you should learn it thoroughly and then refresh your memory from time to time.
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For more mind exercises: http://www.braingle.com/mind/