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Very Easy Logic Problems
A bag of gold coins

Tue May 21, 2013 5:55 am  by chevll

I have 10 bags filled with 10 gold coins a piece, which equals 100 gold coins. 9 bags, are filled with counterfeit coins (90 total coins), while only 1 bag is filled with real coins (totaling 10 coins). They appear the same in shape, color, texture, and size. The only difference is their weight. Counterfeit coins weigh 1oz, while the real coins weigh 1.1 oz. Using a scale, only once, how would I determine which bag was filled with real coins?
Tue May 21, 2013 11:56 am  by vamsikrishna

Tue Jun 04, 2013 3:29 pm  by letmein3

Line the bags up so you don't forget which is which. Take one coin from each bag in order. Keep looking at the scale and add coins one by one. Note each time by how much the scale increases, it should increase 1 oz if you place a counterfeit coin. When it increases by 1.1 oz, take note of the number of the coin you added. Keep adding coins to the end so as not to arouse suspicion. Pretend to do some really complicated mental maths and the stroll over and pick up the bag you noted was different.

Alternatively "use" the scale once to knock out the person owning the bags and take them all. Note: this is a last resort.
Sun Jun 30, 2013 9:26 am  by Maninder

Ha ha ha thats funny...well u dont need to drop down to violence. It will be done in this way....U arrange all bags in a line and start taking out coins from each bag
1 from first bag
2 from second bag
similarly 10 from the last one.
Now put them all on the scale and see the weight.
If all coins would be of 1 oz total sum would be 55 oz.Now since one bag has excess weight coins, so total weight wont equal to 55. It will come out to be...
55.5 if 1st bag has excess weight coins
56 if 2nd bag has excess weight coins
and 60 oz for 10th bag
Thus in this case you can find the bag which contains Heavier coins
Mon May 12, 2014 8:46 pm  by Gurjit

The question is to find the bag with the real coins from among all the other bags filled with counterfeit coins.

Place all the bags divided equally on both sides of the balance scale (5 on each side). One of the sides weighs greater because it has the real coins ([b]1.1 * 10 = 110 oz[/b]). This side exceeds the other side by 10 Oz. Remove one bag from the lighter side and one bag from the heavier side. Repeat this till the balance scales weigh the same. When they weigh the same, the last bag removed from the scale from the heavier side is the one with the real coins.
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