A man has 17 cigarettes.
He gives half of the cigarettes to his oldest son.
He gives one third of the cigarettes to his middle son.
He gives one ninth of the cigarettes to his youngest son.
What brand are they?
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Perhaps they are:
Camel brand cigarettes.
This puzzle is usually posed with camels instead of cigarettes; see here for example.
Also here is the explanation for those who are interested:
1/2+1/3+1/9 = 9/18+6/18+2/18 = 17/18 so the old man would give 9 to his oldest son, 6 to his middle one and 2 to the youngest. 17 in total. 18 is the common denominator between 2, 3 and 9. This way you can divide things that cannot be divided, such as cigarettes or... camels. Apparently it is a famous riddle with camels instead of cigarettes, hence the joke. The trap is that we tend to think in decimals when it comes to dividing non-multiples and so at first it appears to be an impossible problem to solve.
What I especially like here, intended or not, is that the spoiler cartridge looks like a cigarette: