Took two different ancestry tests and they have two different numbers. Why?

All of the tests they give like that have a varience to them. A plus / minus. Its not as exact as one might think. But they both agree that you have a majority of one type of identifier over another.

That's very close in the DNA business. Think about it: you have thousands of ancestors, just the direct lineages, never mind all the other ones. And second, there isn't a single gene for black skin, it's a whole bunch of attributes that may go back to Africa recently or very long ago while blending along the way, and then whatever makes up native American. Native Americans descend mostly from the people who came across from Siberia to Alaska when the last ice age lowered the seas several hundred feet, but there is more and more evidence that other people in small groups came from many other parts of the world too.

To add a little history: our DNA goes back ~70,000 years because most of us alive before that were wiped out then, probably from an enormous caldera (flat kind of volcano). We were in Africa, and if a few had left before then and survived, they were watered down in the DNA record. We were all black, and started migrating towards the east, across to Australia (also a dry land bridge) and China. Europe was settled later because of 2 mile high ice covering it. We moved along shore routes and got to Alaska about 16,500 years ago. By then all the variations in skin color had happened. There's possibly small amounts of mingling of DNA from white Europeans/Vikings etc, Asian mingling from Japan and Polynesia, and other stories (Some Cherokees claim to be descended from a small expedition of Jews). It's a new area of study, relatively, so there is new knowledge all the time.

DNA testing isn't a cut and dry count of genetic markers. It's a comparison of everyone's DNA against each other's. So as the world has more and more testing done, we will be able to tell more and more about who is from where. It's like a jigsaw puzzle with a billion pieces and no picture to use, just the picture you see as you put it together.