History of Space Exploration: Chapter 5, Exercise 2 — Possible Solution
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CORRECTION
Twelve people walked on the Moon, across six successful landings (Apollo
article). Apollo 1 never flew.

CONFUSION
The Saturn V article says the programme landed "24 astronauts on the Moon
across nine missions." Twenty-four appears to count everyone who went to the
Moon, including those who only orbited, but the source does not say, so this is
an inference.