Question About Installing RAM

i have imac 27" i3 mid 2010 4gb of ram. if current ram setup 2x2 (2 sticks of 2gb ram) adding ram in of these ways cause problems?

1 stick of 4gb ram
2 sticks of 2gb ram
2 sticks of 4gb ram

know has been asked wanted clear , specific answer. know how install ram don't understand beyond that.

 

it best install ram in pairs best performance.

here's notes on adding ram apple:

additional notes i5 , i7 quad core imac computers come both top memory slots populated. these computers not start if single dimm installed in bottom slot; these computers should operate single dimm installed in top slot. core duo imac computers should operate single dimm installed in slot, top or bottom. ("top" , "bottom" slots refer orientation of slots in pictures below. "top" refers slots closest display; "bottom" refers slots closest stand).

http://support.apple.com/kb/ht1423?viewlocale=en_us

 

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