We use cookies to personalise content and advertisements and to analyse access to our website. Furthermore, our partners for online advertising receive pseudonymised information about your use of our website. cookie policy and privacy policy.
 
+0  
 
+2
178
1
avatar+194 

  you find 12 coins 

eleven are real gold, one is fake

 

you know the fake weighs a bit less than the others 

 

all you have to use is balance scale

 

what is the least number of times you could use the scale and still determine for certain in which coin is fake?

 Feb 21, 2019

Best Answer 

 #1
avatar+18965 
+4

I think since you know the fake weighs a bit less, it will take 3 tries...

place 6 on each side    the lighter side has the fake

 

take the lighter side    and place   3   on each side

the lighter side again will have the fake

place one of each of these 3 on opposite sides of the scale......if they balance the one NOT on the scale is the fake....

   if they do NOT balance, the lighter side is the fake.

 

 

You COULD get lucky and pick two coins at random and one will weigh less ...if you luckily picked the fake...so in this case it would be ONE try would be the MINIMUM>

 Feb 21, 2019
edited by ElectricPavlov  Feb 21, 2019
 #1
avatar+18965 
+4
Best Answer

I think since you know the fake weighs a bit less, it will take 3 tries...

place 6 on each side    the lighter side has the fake

 

take the lighter side    and place   3   on each side

the lighter side again will have the fake

place one of each of these 3 on opposite sides of the scale......if they balance the one NOT on the scale is the fake....

   if they do NOT balance, the lighter side is the fake.

 

 

You COULD get lucky and pick two coins at random and one will weigh less ...if you luckily picked the fake...so in this case it would be ONE try would be the MINIMUM>

ElectricPavlov Feb 21, 2019
edited by ElectricPavlov  Feb 21, 2019

14 Online Users