Here's why:

* Density: Zinc is less dense than copper. This means that a given volume of zinc will weigh less than the same volume of copper.

* Composition Change: By increasing the percentage of zinc in the penny, you're replacing a heavier element (copper) with a lighter one (zinc).

* Overall Effect: Even though you're using more zinc, the overall mass of the penny will decrease because zinc is less dense than copper.

In summary: A penny with a higher zinc content would actually be *lighter* than a penny with a higher copper content.