# You have fifteen piles of coins, each pile containing twenty coins. The coins appear to be identical in…?

every respect; however, they are not. Fourteen of the piles contain coins that weigh 2 grams each, but one pile is counterfeit, and those coins weight 2.1 grams each. You have at your disposal a single pan scale, such as is used to weigh produce, and your problem is to determine which of the piles contains the counterfeit coins, using the scale once and only once. You may not add or take away coins once they have been placed on the scale.

You take one coin from the first pile, two coins from the second pile three coins from the third pile, and so on, taking fifteen coins from the fifteenth pile and placing them on the scale. If all 120 coins now on the scale weighed 2 grams each, the pile would weigh 240 grams. However, it will instead weigh anywhere from 240.1 grams to 241.5 grams, depending on how many counterfeit coins are on it.

If it only weighs 240.1 grams, there’s only one counterfeit coin on the scale, so the counterfeit pile is the first one, from which you took one coin. If it instead weighs 240.2 grams, there are two counterfeit coins on the scale, so the counterfeit pile is the second one, from which you took two coins, and so forth.

uhhhh I think your on the wrong category

easily… place each pile and record. once I put a pile that is counterfeit I will know because a .1 will appear in the weight scale.

Ex. X fills the spot, the number left of it indicates what pile.

1) 1x

2) 2x

3) 3x + .1

4) 4x + .1

5) 5x + .1

I will know that pile 3 is counterfeit because it disrupted the weight.

That or I’ll place all of the coins into one big pile on the scale and say that, that’s the pile with the counterfeit coin.

1: Why can you only use the scale once?

2: Why are you using a produce scale to measure money?

3: Why is this problem so hard?

4: What kind of coins are they (Country,year, style, etc.)

5: Don’t counterfeit coins have incorrect stuff on them?

hard enough 2 answer