|The moon (in case you aren't sure what we're talking|
about). Image from Wikipedia
'It took less than 40 years to put a man on the moon.''Really? did it really? And how the heck did you work that out?' I nearly shouted.
Leaving aside whether or not it should have been 'fewer than 40 years', let's try to pin it down. The first manned moon landing was 1969, so assuming 'less than 40' is 30-39 years that puts us approximately between 1930 and 1939. I'm struggling to find anything that fits that date. Tsiolkovsky's Investigation of Outer Space Rocket Devices was published in 1903, Goddard was flying rockets by 1915 and published his paper A Method of Reaching Extreme Altitudes, where he suggested a rocket would reach the moon 5 years later. And, of course, rockets themselves had been around far longer.
Putting aside the age of Homo sapiens as the best 'it took n years...' date (after all, you can't put a man on the moon without a human), I'd say there are only really two sensible time periods. It's either 8 years - the time between Kennedy's 'this will be done in the decade of the sixties' speech and the landing, or it's around 280 years from Newton's Principia being published, as that provided all the science required and the rest was just a matter of engineering.
I don't offer these periods seriously, but rather to illustrate what a daft idea it is to say 'it took less than 40 years...' History rarely works like this - history of science and technology even less so. As statistics go, it's moonshine.