OK., so we have these twelve islanders,
Andy, Barry, Cliff, Darius, Ernie, Frank, Geoff, Harry, Isaac, Jacob, Kevin and Larry.
Eleven of them have the same weight but the twelfth, and we don't know which, is either lighter or heavier than the others.
We have to find the odd one out by the use of a see-saw which we are allowed to use just three times.
We let them take turns as follows.
First go { Andy, Barry, Cliff, Darius} V {Ernie, Frank, Geoff, Harry}
Second go {Andy, Harry, Kevin, Darius} V {Isaac, Frank, Jacob, Cliff}
Third go { Isaac, Barry, Geoff, Harry} V {Larry, Darius, Frank, Jacob}
By noting what happens at each turn we can always work out which is the odd one out and whether he's
lighter or heavier.
BTW., don't confuse Barry, Harry and Larry, it mucks up the whole thing if you do.
Here's an example of how its works, (though there are a number of variations in the reasoning).
Suppose that Ernie is heavier than the others.
What will happen is that at the first go, the right hand side will go down.
That means that either one of Andy, Barry, Cliff or Darius is lighter, or one of Ernie, Frank, Geoff or Harry is heavier.
At the second go, the see-saw will balance.
That means that they are all of the same weight and can be removed from the 'first go' list.
We are left with either Barry being light or one of Ernie or Geoff being heavy.
At the third go they balance again so that lets us remove Barry and Geoff.
We are left with Ernie being the heavy one.
Here's three others to try.
(1) Left down, Left down, Balance.
(2) Balance, Left down, Right down.
(3) Right down, Right down, Left down.
Tiggsy
