Homework Help: math

Posted by claudia on Sunday, January 22, 2012 at 2:26am.

In a group of 9 coins, one is fake and weighs slightly more. What is the fewest number
of times you need to use a pan balance to find the counterfeit coins? (A pan balance is
a scale used to measure weights, where weights are placed in two pans. The heaviest
pan will go down and the other up.)

math - drwls, Sunday, January 22, 2012 at 3:19am
This puzzle has been answered mnay places online. Two weighings are sufficient. This answer is copied from one site easily found:

"Divide them into three sets of three. Weight two of the sets. From that you can determine which of the three sets contains the light coin.

Then take that set and weigh two of the coins. If the scale balances take the lighter coin, otherwise take the coin you didn't weigh."

Answer this Question

Related Questions

MATH - There are 10 similar coins, but 2 of them are fake. The fake ones are ...
math - suppose you had $1.76 in dimes and pennies. What is the fewest number of ...
algebra - How many coins When i dumped the change out of my pocket, I noticed ...
Math - Steven has 9 gold coins that are identical in appearance. However, one ...
PROBLEM SOLVING IN MATHEMATICS - you have 13 bags of gold wins. out of 13 bags ...
PROBLEM SOLVING IN MATHEMATICS - you have 13 bags of gold wins. out of 13 bags ...
4th grade - how can the clerk make the change of the $1 bill using the fewest ...
Math - Susan has some $2-coins and $5-coins. If there are 18 coins and the total...
Math - Shirley has 18 coins. One sixth of the coins are quarters, one third of ...
Math,Ratio - the ratio of the number of coins Azam had to the number of coins ...

For Further Reading

First Name:
School Subject:
Answer: