What is the difference between "I don't know" and "I didn't know".
What is the difference between "I don't know" and "I didn't know".normally,which should be said when someone don't know about something.

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"I don't know" means you don't have the knowledge at this time, but "I didn't know" indicates that you DO know now, but did NOT know at some previous time.

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I DONT KNOW .. in present tense which the action happens in the present " i dont know now "
I DIDNT KNOW .. in the past tense which the action happend in the past " i didnt know yestersay .."

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They have the same meaning. We use i dont know in present time, and i didnt know to show past time.

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i do not know - i don't know
i did not know - i didn't know 
or *i did not knew*
I sware, I sware, I didn't knew what happend.
I sware, I sware, I don't know what is happening.
sorry I didn't thrust you
sorry I don't thrust you
hope you se the differance.

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Thank you  for every one answer my question.