# eight balls - puzzle

murrow
Posers and Puzzles 01 Feb '05 15:52
1. murrow
penguinpuffin
01 Feb '05 15:52
apologies if this has appeared before

you have eight balls, they all look and feel identical. however one of them weighs slightly less than the others (you can't tell by holding them).

you want to work out which is the lighter ball.

all you have is a pair of ballancing scales (ie tells you if stuff on one side weighs the same as stuff on the other side).

you can fit as many balls as you like on the scales.

how can you find out for sure (ie not relying on luck) the identity of the lighter ball IN THE LEAST NUMBER OF WEIGHINGS?
2. genius
Wayward Soul
01 Feb '05 16:02
weigh 4 against 4. take the 4 on the lighter side, and weigh two against two. then one against one. that's 3 weighs...
3. Acolyte
01 Feb '05 16:33
Originally posted by murrow
apologies if this has appeared before
Indeed it has. In fact, I was thinking of compiling a 'Posers &amp; Puzzles FAQ' section on my website, including a general approach to the balance problem. In this case, the answer is that 2 weighings are needed, but I'll leave others to explain why.
4. genius
Wayward Soul
01 Feb '05 17:01
okay-3 against 3. if they balance, weigh the remaining two. else, weigh 2 from the lightest side against each other. if they balance, it's the other one from that side. and if they don't, the lightest one is -well- the lightest one! ðŸ˜€
5. 01 Feb '05 17:051 edit
3*3
if equle, then the other two for an answer.
if one is less, then of the lighter, 1*1
if equle, then the one left out
if one is lighter, then that one.

6. murrow
penguinpuffin
01 Feb '05 18:05
yup, that's it (you both are saying the same i think)ðŸ™‚