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Probably not worth it, you may get 10 or 20 € for it, if at all.
Keep the memory in a dry place in case you ever need to bring your Mac to Apple or any authorised repair centre, because sometimes it happens, that Macs get handed back with the original amount of RAM and the original HDD.
 
I'd say save it for the purposes 'simsaladimbamba' stated. I got a measly $0.99 when I sold a 1x2GB RAM stick pulled from a MBP on eBay.
 
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