חידה קשה

[nahemmm]

חידה קשה

יש 12 מטבעות. 11 באותו משקל ו-1 שונה במשקל מהאחרים (או שהוא שוקל פחות או יותר, לא ידוע). בעזרת 3 שקילות במאזניים צריך למצוא את המטבע השונה. חידה קשה מאוד. רק גאונים יכולים לפתור אותה.

 

[hillelgoral]

answer

i will number the coins 1-12 and only take into account the worst case scenario... so, first i will weigh 1-4 and 5-8. assuming they are not the same, i will take coins 6,7,8 out and put coins 9,10,11 instead of them and also swith coins 4 and 5. if the two groups are the same, i know the fake is 6,7,8 and i know if its heavier or lighter (depends how the group the weighed compared on the scale. if the outcome did not change, i know its 1,2,3 and again i know if the fake is heavier or lighter and if the outcome changed, i know its either 4 or 5, and by comparing one of them to a good coin, can determine which one is the fake.

 

[nahemmm]

כמה שאלות בקשר לפתרון

מה עם מטבע 12? ולמה אתה לא כותב בעברית

 

[nahemmm]

אהה הבנתי מה קורה עם ה 12...

פתרון גאוני.

 

[hillelgoral]

also possible with 13 coins

the reason is that i'm not in israel, so with some computers i cant, and the others dont have hebrew on their keyboards. also, the smae riddle, but with 13 coins and 3 weighs, is also possible.

 

[hotel]

אי אפשר עם 13

אי אפשר עם 13 כי לא ניתן לדעת אם המטבע כבד יותר או קל יותר

 

[hillelgoral]

13is possible

you devide the the 13 into 4-4-5 and weigh 4-4 first. if they do not weigh the same, than the way to find out is posted above. is they are equal, you take 3 good coins against 3 you are not sure about. if they do not weigh the same, you 3 that you know one of them is fake, and you know if the fake wighs more or less and most important you have one more weigh... if the 3 weigh the same as the good three, you compare one of the 2 to a good coin... and there, you found the fake out of 13 with only three weighs.