In a manner based on or using the duodecimal system; by means of base-12 mathematics.
From duodecimal + '-ly' (adverb suffix). The '-ly' suffix transforms adjectives into adverbs, indicating the manner or way something is done, similar to 'quick' becoming 'quickly.'
If you performed a calculation duodecimally, you'd be doing arithmetic the way ancient Babylonians did—switching your brain from the base-10 system your fingers taught you to think in base-12 instead, which might actually make division problems easier!
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