Answers

2014-08-02T22:08:10+08:00
Doing nothing - You are not doing anything.
Doing for nothing - You are doing something for nothing. For something that is not important.
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2014-08-03T15:03:53+08:00
"Doing nothing" is not doing anything for any type of activity, it's simply idle.
"Doing for nothing" is doing something that for no type of reason, or a useless thing.
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