I had to think about this for a bit because it sounds so natural to me that I hadn't ever thought about it. It's expressing the comparison in terms of a trade, in my opinion.
If I want to bargain in a market, I might say:"I'll give you seven dollars for two of those." I'm trading seven dollars for two items. In this case, the speaker is talking about memories as if he were able to trade them. "(I could trade you) ten for every one of yours." When sharing memories, we actually speak of it sometimes as "swapping memories", as if we're trading them like goods or currency.
That's my interpretation, at least.
Just out of curiosity... were you expecting "Ten to every one of yours"? That's the only other word I could think of in that position and it's less idiomatic than "for", in my opinion.
Thank you for your reply~!
Sorry, I cannot provide more context right now.
But i guess it thought it's something like "I memorized ten words for every one word you did" (the speaker is saying he has a good memory)
And then, I cannot determine the meaning of "for"