i soRt of have a puzzle here.. if you r free, nothing to do, try to solve it lor.. keke... all thE bEst!
Puzzle
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I have 12 bags of coins: 11 bags contain real coins, and 1 bag consists of fake coins. (num of coins in each bag may not be the same)
Each real coin weighs 10g but on the other hand, each fake coin weighs only 9g.
What is the least num of times i have to weigh, before i can find out which bag consists of the fake coins?
If you say is 'x' (where x is any positive num) num of times, whY?
By the way, the answer is definitely less than 12. That is, x < 12.
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This will probably be my last post before the exams end..
only 3-4weeks to exams le.. *nervous*
if someone can solve it, then gd lor.. hee~ but if no one can solve, of course i will give the answer, but.. after exams ba.. =p
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6 comments:
well, u din say to weigh the entire bag rite? haha.. so, juz take individual coin out from each bag n weigh la! =P in tt case, definitely less than 12 tries! =P
if not ah.. juz take one real coin n chuck it together w each bag u wanna weigh.. so long as e weight shows an odd number, tt's e bag of fake cOins! =P still less than 12 tries! =P
ah...wat e heCk.. tink e sun's gotteN into me n it's makin me not able to comprehend ur qns properly!
it can be bingo on the first hit!
well, exaMs coming? jiayOu o! all e best n taKe care lots.. =)
ok.. both of ur ans quite close la.. but u no explain clearly.. anyway, so exactly how many tries? cuz i told u ans is less than 12, so telling me tt the ans is less than 12 doesn't say anything leh.. =p
oh btw, u can only put things on the scale once. u cannot like put one coin first, then dun remove the coin and keep adding.. its illegal!! haha.. each time the scaling needle moves consider 1 weigh.. so ur 2nd post ans is wrong lor.. 1st post.. like also wrong leh.. =)
oK..wRong jiu tink again! haha.. neveR say die.. =P
answer: ONE try... =P
how: take 1 coin from 1st bag, 2 coins from 2nd bag, 3 coins from 3rd bag, blah blah.. 12 coins from 12th bag.. and weigh altogether..
so... 2 ways u can see which is e bag of fake coins..
1)if ALL are real, shld weigh 780g.. if u get a reading of eg. 775g, u noe it's short of 5g so it's e 5th bag tt is fake.. reading of 772g means 8th bag is fake..reading of 770g means 10th bag is fake.. 768g means 12th bag fake..
2)long-winded way to manually count out all if so kiasi kiasu.. so, 1st bag fake=779g, 2nd bag=778, 3rd bag=777, blah blah, 12th bag=768.. then see which coincides.. =D
shoOts..i seem to be e only bOliaO person answering u huh..but but.. not tt im so fRee nothg to do.. i juz need a channel to destress due to e overloadin of DEADlines ive gotta meet..! argghh... =P
shld be coRrect this time le ba? else i'll start gg bald from all e hair-tuggin..
once again, jiayou fOr ur exams n soOn, sch will be over! =)
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