Not really a senior moment, Margot. The question was asked incorrectly. Twenty is not slang for a score; score is slang for twenty. The question should have been "For what number is score the slang?"
In fact it is arguable that "score" is not slang at all (in the same way that "gross" - 144 - is not). I believe its original use in Old English was something to do with counting sheep. When twenty had been counted a mark was scored on a tree to keep the count. It's where "scoreboard" and "scorecard" originate.
Proper slang terms for numbers (usually money) include a "pony" (£25) and a "Monkey" (£500).
I wouldn't refer to a score as slang either (except when £20 is referred to as a score, perhaps) so maybe the question has been mistranslated/mistyped at some point.
A jackson is slang for $20.
The slang for £20 is Bobby Moore or Apple Core
>The original question made no mention of money.
Agreed, NJ. But the original question didn't make sense, as you intimated at 15:36, so some of us have suggested what the OP may have been trying to ask. I think you were the first one to refer to slang terms for money and some of us picked up on that