Hint
How many large pipes are required to drain the reservoir in 24 hours?
Answer
21 hours and 36 minutes.
Reasoning
Looking at the first clue:
in 12 hours, 6 large pipes can drain 1 reservoir
in 24 hours, 6 large pipes can drain 2 reservoirs
(*) in 24 hours, 3 large pipes can drain 1 reservoir
Looking at the second clue:
in 8 hours, 3 large + 9 small pipes can drain 1 reservoir
in 24 hours, 3 large + 9 small pipes can drain 3 reservoirs
But, by (*), we know that in those 24 hours, 3 large pipes can drain 1 of those reservoirs.
Therefore, the other 2 reservoirs can be drained by the small pipes on their own:
in 24 hours, 9 small pipes can drain 2 reservoirs
in 24 hours, 1 small pipe can drain 2/9 reservoirs
multiply the hours by 9:
in 216 hours, 1 small pipe can drain 2 reservoirs
in 216 hours, 5 small pipes can drain 10 reservoirs
divide the hours by 10:
in 21.6 hours, 5 small pipes can drain 1 reservoir
21.6 hours = 21 hours and 36 minutes.
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Puzzle 19
Look at the following sentence once, and once only. How many times can you find the letter F?
Furry foxes of far origin often come of age far before scientific study forecasts.
Once you have unscrambled the following countries, the first letters can be anagrammed to make a hidden country. aadnorraehiioptceeegraaaacdgmrsanorwyaaimnoreemny
Reasoning aadnorr = Andorraaehiiopt = Ethiopiaceeegr = Greeceaaaacdgmrs = Madagascaranorwy = Norwayaaimnor = Romaniaeemny = Yemen
a + e + g + m + n + r + y = Germany.
