There are 10 stacks of coins.
Each stack is made up of 10 coins.
All coins looked EXACTLY the same.
Out of the 10 stacks, one stack of coins is made up of 0.1g lighter coins as compared to the other coins in those 9 stacks.
In another words, Each Coin in Those 9 Stacks weighed 1g...
But Each Coin in that 10th Stack weighed 0.9g
You have an electronic weighing machine which you can use only ONCE.
How are you able to know which stack is the stack which consists of the lighter coins? (i.e. the stack which is made up of the 0.9g coins)
*** Updated on 5th November 2009 @ 11.37pm:
EVERYONE gave me the same WRONG answer.
So let me clarify it here.
Once you put the coins ON the weighing machine, you CANNOT touch the coins anymore and IMMEDIATELY will know the answer.
*wink*
Think again!
7 comments:
hmm..can i play cheat???
i put all 10 stack on the electronic weighing machine and remove one stack at a time. So each time i remove one stack of coins, the "drop" in weight should be 10g. If the "drop" is only 9g, that stack that was removed is the stack with lighter coins..
hee..i know, i'm a cheater..
*huge laugh*
EVERYONE gave me this answer!
Wrong!
Once you put the coins ON the weighing machine, you CANNOT touch the coins liao and IMMEDIATELY will know the answer.
*wink*
Think again!
wad abt doing it the other way round?
put one stack at a time and see the increase?
Simple, Stack 1 take 1coin, Stack 2 take 2coins, Stack 3 take 3coins..and so on till Stack 10. Total u've taken 55coins, put them on the scale.
By right if each is 1g, then u shld hve 55g. But coz they are mixed with 0.9g coins so the weight will be lower.
55g minus (weight shown), using the decimal number, will indicate the number of 0.9g coin/s on the scale. That stack is the lighter stack.
Example: If 2coins is 0.9g each, total weight for the 55 coins will be 54.8g
55g - 54.8g = 0.2 , take the decimal number as reference, Stack 2 is the 0.9g stack OR 2coins on the scale is the 0.9g stack.
*clap clap clap*
The 'winner' goes to Mark!!!
but no prize. *giggle*
Post a Comment