Installing RAM in pairs. What about 3 gb?

hi. We all know that ram has to be installed in pairs… How does that work for 3 gb? Will a pair of 2gb and 1 gb work or can we install 3 separate 1 gb sticks?

i got a lenovo core2duo pc with Intel inside.
Added (1). i have 4 RAM slots.

Read more: Installing RAM in pairs. What about 3 gb?