I found money in my purse

I usually don't lose money in my purse. I usually know exactly how much I have within a few dollars. Yesterday I reached into my purse during lunch for a dollar because I wanted a piece of fruit. Imagine my surprise when I pulled out a $20 dollar bill along with the $1 dollar bill. I don't remember when I took the money out of the bank or when I put it in my purse.

I wonder where it came from or how long it was in there.