Such figures are letters (5,7)

I believe the answer is:

roman numbers

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'letters' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'such figures' is the wordplay.
'such' becomes 'roman' (I can't explain this - if you can you should give a lot more credence to this answer).
'figures' becomes 'numbers' (I've seen this before).
'roman'+'numbers'='ROMAN NUMBERS'

'are' acts as a link.

Can you help me to learn more?

I've seen this clue in The Globe and Mail.

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