We have 12 Coins.
One of them (we dont know which one?) has different weight from the others.
With three time scaling (the scale has two pans) find the differrent coin.
source:mathlinks
1man this question is for the lucky person
supposing i am lucky
just divide the coins into 3 groups of 4 each
weigh the first two groups.....and u find them equal
my luck comes into play here
then u know that the faulty coin is in the third group
now weigh two-two coins from that group together and from that we can find out the faulty coin.........
but its not zaruri that i get the wrong coin in three steps.......
11is this question from the Russian book they give on qualifying in RMO ??
correct solution is i think what arshad has said ..
1but my solution depends on luck and since when has mathematics started depending on luck???
23@ arshad elaborate the last part ........
if we weigh 2 -2 coins and suppose LHS wala 2 coins are heavier .......so wat would u say wich set has the abnormal coin??here it isnt given that the abnormal coin is heavy or light
23@ injun i think u didnt get wat i m trying to say ....
see suppose the 2 grps u take first are unequal in weight ...so wat will u conclude .... faulty coin is in the heavier group or lighter group??? faulty coin is heavy or light ye diya nahi hai ...
btw i m getting it in 4 steps [102]
1357Actually here it is not mentioned that the faulty coin is heavier or lighter.
So its difficult in 3 scalings
Ok let's find out how many minimum scaling required for finding the faulty one
39no manish, 3 are enough..
this was one from a old forum which i particularly found interesting while i was going through the old posts,, so gave it here.
here`s the link:
http://www.mathlinks.ro/viewtopic.php?search_id=717924636&t=49152
1supposing the odd one to be heavier
frst divide into two groups.......6 each..... nw take the heavier grp and divide into 2 grp of 3 and weigh.....so we hav already used the scale twice..... nw ttake the heavier grp and divide it into 3 grps with one ball each.....take any two balls and weigh them thus using the scale for the 3rd time...... if either of the ball is heavy then, then we have found out the faulty ball......if both are of same wt then the 3rd ball is the faulty one......
so where m i wrong?????????????
