Please help me on this question it's like about pennies and the mass and I don't know just look?

Question

We found that pennies can be put into 2 different groups by mass. Why are there 2 types of pennies and when did we chagne how they were used. Please help I'll really appreciate it!

Answer 1

Hi. Pennies used to be made of almost pure copper but the cost of making them was more than they were worth. The alloy was changed. Just do a search on 'penny alloy'.

Answer 2

my guess would be that older pennies are made of pure copper and newer pennies are made from a composite copper which is lighter I think this happened in the late 70's