There were people in my algebra class that didn't know how to add negatives.
I would laugh but I struggled for a bit when I got into Intermediate Algebra. They let me pass a few classes because of my grades in highschool math but I can tell you that 9 years of not really using a majority of that stuff left me feeling puh-retty stupid.
Hell the first time I saw a negative exponent after coming back to college I thought my teacher had made a typo on the assignment he gave us lol.