plz help

[skillszone]

There are 9 coins. Out of which one is odd one i.e weight is less or more. How many iterations of weighing are required to find odd coin?

[FoxLee]

Three?

l. Weigh two lots of 4 coins (it could be that they're exactly the same and the 9th coin would be the heaviest)

2. Assuming not, split the heavier of the 4's into 2

3. split the heavier of the 2's into one each side of the scale

[bongerman]

The answer is three but is more complicated than Fox'a answer.

Fox - in your example in your second weighing when one side goes down you don't know if that's due to a lighter coin being on the light side or a heavier coin being on the heavy side.

To start though call the coins 123456789:

Weighing 1: 123 v 456
Outcome 1a: level..... odd coin is in 789
Outcome 1b: LH down... either heavy coin in 123 or light coin in 456
Outcome 1c: RH down... either heavy coin in 456 or light coin in 123

.....