The 33 1/3 second mystery #6
 

I have ten bags of coins, each bag containing twenty coins. One bag contains counterfeits which weigh 1 gram more than the authentic, which weigh 10 grams each.

Using a digital scale, how can I determine which bag contains the counterfeits with one weighing?

set each bag on the scale one at a time and wacth the weight after putting a bag on. once you see the total weight increase by 11 grams, you've got your winner.

Thats not one weighing.

Put 1 coin from the first bag, 2 coins from the second bag, 3 coins from 3rd bag,....etc... onto the scale, and do one weighing.

If its x grams overweight, then the xth bag is the counterfeit bag...

I'm assuming that each coin weights 10 grams here, and each counterfeit coin weighs 11 grams.

Put all the bags on the scale at once. Then watch the scale as you remove them. When it jumps down 11 extra grams you know that the bag that was just removed is the winner

Why couldnt it be one weighing if you placed the bags on one at a time? Eventually, you would have to have all the bags on there to get the total weight (hence one weighing).

Thats just a way of getting around the question. I know i didn't ask this question, but lets say that this particular scale has a button that you press to display the weight, and you can only press the button once.

My method allows you to consolidate everything, you can even mix all the coins up in a basket, and truly weigh it at one shot.

dimbulb gets the fuzzy bunny for this round.

Dog my cats, you folks answer these quickly! :eek:

Hopefully the next one will keep you all going for a few days while I'm away from the PC. :)