How much does a penny weigh?

On Friday the tenth of September a question was asked by Dr. Schultz to determine the weight of a penny that we had found on the ground.  To find the answer I simply googled the average weight of a penny, and found that a penny weighed 2.5 grams.  On Monday the 12th two more questions were asked.  One about the weight of a penny in the 1970's and the other about the weight of a penny in the early 1700's.  We then were split up into groups to come up with our best response to the questions.  First, to figure the weight of a average penny we weighed five on a scale and took the average.  To find the weight of a penny in the 1970's we found 5 pennies from that era and weighed and averaged their amounts.  The two answer varied, because of the composition of the penny from the two different time periods.  We then researched the composition of a penny from the 1700's, and found that they were made of pure copper.  With this information we were able to estimate its weight.  We also thought about the first question more indepth.  If we had picked up a random penny it could either way 2.5 grams if it was made after 1982, or 3.2 grams if it were made before 1982.  We then took a sample of 100 pennies to see how many were pre and post 1982 to find which penny you would have a greater chance of finding on the ground.