Jump to content


Welcome to BrainDen.com - Brain Teasers Forum

Welcome to BrainDen.com - Brain Teasers Forum. Like most online communities you must register to post in our community, but don't worry this is a simple free process. To be a part of BrainDen Forums you may create a new account or sign in if you already have an account.
As a member you could start new topics, reply to others, subscribe to topics/forums to get automatic updates, get your own profile and make new friends.

Of course, you can also enjoy our collection of amazing optical illusions and cool math games.

If you like our site, you may support us by simply clicking Google "+1" or Facebook "Like" buttons at the top.
If you have a website, we would appreciate a little link to BrainDen.

Thanks and enjoy the Den :-)
Guest Message by DevFuse
 

Photo
- - - - -

Weighing I.


  • This topic is locked This topic is locked
27 replies to this topic

#1 rookie1ja

rookie1ja

    Senior Member

  • Site Admin
  • PipPipPipPip
  • 1338 posts
  • Gender:Male
  • Location:Slovakia

Posted 30 March 2007 - 06:00 PM

Weighing I. - Back to the Water and Weighing Puzzles
You have 10 bags with 1000 coins each. In one of the bags, all coins are forgeries. A true coin weighs 1 gram; each counterfeit coin weighs 1.1 gram.
If you have an accurate scale, which you can use only once, how can you identify the bag with the forgeries? And what if you didn't know how many bags contained counterfeit coins?

This old topic is locked since it was answered many times. You can check solution in the Spoiler below.
Pls visit New Puzzles section to see always fresh brain teasers.


Spoiler for Solution


Spoiler for old wording

  • 0

rookie1ja (site admin)
Optical Illusions
Support BrainDen

"To start: Press any key... Where's the 'any' key?" - Homer Simpson


#2 kola

kola

    Newbie

  • Members
  • Pip
  • 4 posts

Posted 20 April 2007 - 05:33 PM

If we dont know how many bags has faulty coins, then min number of coins from bag i = 2 * number of coins in bag i-1.

Therefore, the sequence would be

1, 2, 4, 8, 16, 32, 64, 128, 258, 512.

Basically, represent the weight difference divided by 0.1g in binary numbers and positions of 1 will give you which bags have faulty coins.
  • 0

#3 vinay0007

vinay0007

    Newbie

  • Members
  • Pip
  • 4 posts

Posted 08 May 2007 - 02:44 PM

Binary series is more precise.. which depicts.
2^0, 2^1, 2^2.... so on.
and whatever the extra weight it will be simple for the calculation..
100101010 format
  • 0

#4 Garrek99

Garrek99

    Junior Member

  • Members
  • PipPip
  • 60 posts

Posted 17 May 2007 - 12:56 AM

This sequence won't work:

1, 2, 4, 8, 16, 32, 64, 128, 258, 512.

Here is why. If the 10th bag only is full of fakes you'll get an extra weigh amount of 51.2g.
And, if bags 2-9 are fake then you'll get (25.8+12.8+6.4+3.2+1.6+.8+.4+.2) 51.2g and then you won't be able to tell which situation you are in.

The total extra sum has to be distinct for any combo of fake bags.
  • 0

#5 Baikin

Baikin

    Newbie

  • Members
  • Pip
  • 4 posts

Posted 29 May 2007 - 06:34 AM

There's a mistake on that sequence, so there's also a mistake on proving it wrong.

The sequence should be:

1, 2, 4, 8, 16, 32, 64, 128, 256, 512, and so on. This sequence should meet the mentioned conditions.
  • 0

#6 Camshaft

Camshaft

    Newbie

  • Members
  • Pip
  • 5 posts

Posted 03 July 2007 - 07:35 PM

Place all bags on the scale, it should read 10,100g. Take off a bag until the 100 at the end goes away. That will be the bag with the forgeries. If you don't know how many bags contain the forgeries, then still place all bags on the scale and every time 1,100g is removed from the weight that bag will be full of forgeries.
  • 0

#7 Garrek99

Garrek99

    Junior Member

  • Members
  • PipPip
  • 60 posts

Posted 09 July 2007 - 12:26 AM

Place all bags on the scale, it should read 10,100g. Take off a bag until the 100 at the end goes away. That will be the bag with the forgeries. If you don't know how many bags contain the forgeries, then still place all bags on the scale and every time 1,100g is removed from the weight that bag will be full of forgeries.



You are given one opportunity to use the balance. Your method requires 1 or more tries.
  • 0

#8 puppyluv1725

puppyluv1725

    Newbie

  • Members
  • Pip
  • 1 posts

Posted 21 July 2007 - 06:15 AM

you know
all these weird riddles and stuff make my brain hurt like heck
can you make them a bit clearer and not so hard :o
  • 0

#9 pilgrim

pilgrim

    Newbie

  • Members
  • Pip
  • 4 posts

Posted 12 October 2007 - 09:42 AM

It's a good one
  • 0

#10 luioliher

luioliher

    Newbie

  • Members
  • Pip
  • 3 posts

Posted 20 November 2007 - 03:45 PM

You can always open the bag :D
  • 0




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users