This question already has an answer here:

This is an easy one - a more interesting one is in the works!

A party is being held at a local mansion. The host is very rich and his success is because of one thing - his famous recipe for spaghetti.

The only guests that may attend are people who correctly reply to the guard at the door.

You are trying to gatecrash the party in order to steal the recipe. You sneak by and listen to the passwords, hoping to guess the pattern.

The first guest arrives. The guard says "3". The guest replies "5" and is admitted.

The second guest arrives. The guard says "1". The guest replies "2" and is admitted.

The third guest arrives. The guard says "12". The guest replies "9" and is thrown into a tank of red herrings to be devoured.

The fourth guest arrives. The guard says "21". The guest replies "7" and is admitted.

You walk up and get a "20" from the guard. What should you say?


marked as duplicate by skv, Mathias711, Kenshin, Florian F, mdc32 Nov 16 '14 at 19:35

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  • 1
    $\begingroup$ I was hoping this one would involve rule 34 somehow... $\endgroup$ – Michael Nov 15 '14 at 23:58
  • $\begingroup$ hints please :D $\endgroup$ – Kelvin Barsana Nov 16 '14 at 0:19
  • $\begingroup$ Is the part about the red herrings just a red herring? $\endgroup$ – HDE 226868 Nov 16 '14 at 1:10
  • $\begingroup$ @HDE226868 - yes :-) $\endgroup$ – Rand al'Thor Nov 16 '14 at 11:40
  • $\begingroup$ I didn't realise this was a duplicate! (I haven't actually bothered reading all the old 'Security to the Party' questions...) Should I delete the question? $\endgroup$ – Rand al'Thor Nov 16 '14 at 11:41

The logic seems to be

counting the number of segments required to show the numbers in a digital board

Going by the above logic 20 requires 2 and 0 - 5 segments needed for 2 and 6 for 0. Totalling to 11 as the answer

  • $\begingroup$ Please do not post an answer where all the content is hidden in spoiler markup. Your answer should make sense and be distinguishable from another answer to a reader who cannot or chooses not to read the spoiler block. $\endgroup$ – Gilles 'SO- stop being evil' Nov 16 '14 at 12:00
  • $\begingroup$ @Gilles and hence the downvote? $\endgroup$ – skv Nov 16 '14 at 12:23
  • $\begingroup$ @skv - Gilles is going around downvoting everyone whose answers are spoilers :-( $\endgroup$ – Rand al'Thor Nov 16 '14 at 12:27
  • $\begingroup$ Ha ha ha ... if he/she believes that improves the overall experience of the site, he/she is well within his/her rights to do so, and while the whole idea of spoiler is to avoid an accidental view of the logic and with the edit I have followed all the guidelines provided in the link he mentioned, at the end of the day this is a duplicate question (I have voted for it to be closed) so its ok I really dont feel like taking more credit on this in any case $\endgroup$ – skv Nov 16 '14 at 12:31

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