Quality Testing

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1.  You have a weighing machine, and you have 27 balls in which 26 balls are of same weight and 1 ball is of different weight. How many times/steps needed to identify the 1 ball which is different from other ball?

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If thats the case I believe it will not be solved :)
it can be in 4 steps as explained on page 1 in the 3-groups-methods
how do you know that defective ball is heavier??????
First 27 balls will be grouped into 3 equal sets and each set will be weighed. Surely one set will have more/less weight. Now this set (9 balls) will be grouped into 3 equal sets and each set will be weighted again. now one set (3 balls) will have more/less weight. now these 3 balls will be weighed and finally we can identify the different ball.

so totally 3+3+3 = 9 times/step are required to identify the different ball.
it is only 4 step method brother y didnt u see mine and tim's post on first page

Maximum it will take 4 steps...

27= 13+13+1(weigh 13 13 group. if equal the remaining ball is heaviest, else next step)

13=6 +6+1 (weigh 6 6 group. if equal the remaining ball is heaviest, else next step)

6=3+3(find the heaviest group)

3=1+1+1(weigh just two balls ...we will find  the answer)

Thank u..

same answer as vamshi and still not correct ;)
hey tim now i m sure that only mine and u is proper answer and it is not more then 4 steps   hahahahha

whats wrong in that?

can u tell pls.

see the discussion with vamshi (begins on page 2)

I can't get anything from that discussion?

can u pls make it clear to me where i m wrong.

Thanks.

it is nowhere said, that the defect ball is heavier. it could also be lighter than the other ones.

so you don't know which group of 13 balls you have to take for the next step.

Example:

27 = 13+13+1 = grp1 + grp2 + 1

grp1 < grp2
if the defect ball is heavier you would take grp2, otherwise grp1. BUT you DON'T know what the defect is, so you don't know if you must choose grp1 or grp2.