How old was Melvil Dewey when he created the Dewey Decimal System?

Answer:

Dewey was born on 10 December 1851. His book was published before April 1876. He would have been 24 at that time.

Lydenberg, H.M. Dewey, Melvil. Dictionary of American Biography. New York: Charles Scribner's Sons, 1944. Suplement I; pp 241-243.

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