Coin Isotope

1. Weigh 10 pennies dated 1982 OR 10 pennies from a mixed group. These pennies represent an element with two different isotopes.

   ______________g is the average weight of these pennies

2. Next get the weight of pre and post-1982 pennies.

   ______________g is the average weight of ten pre-1982 pennies called X.

   ______________g is the average weight of ten post-1982 pennies called Y.

   Use the following formula to determine the percent of the 1982 pennies (mixed group) that represent the pre-1982 type and post-1982 type.

   avg. wt. 1982 coin = ag. wt. X + avg. wt. Y

   in place of Y use (1 - X because Y can be determined by subtracting X from 100%.

   Solve for X

   round to nearest 10%

   solve for Y

Conclusion

1. If you worked with the mixed group of pennies to start with, does your percentage of pre-1982 pennies determined by the formula agree with the number you actually started with?
2. Why is the average weight used instead of the weight of ten coins?
3. What is the difference between pre-1982 and post-1982 pennies? Try some chemical tests to find out.

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