I went to a review tonight that was led by one of the TAs (or teaching assistants) meant to prepare us for our upcoming midterm exam.
A girl came up to the board to work out a sample problem. In the course of this, she had to add 0.25 and 0.5, which one might assume would lead her to answer 0.75. FALSE. What did she write?
0.25 + 0.5 = 0.3
Our TA gave us an example of a reaction taking place in deionized water. A girl raised her hand and looking quite concerned said "Can you drink that? Isn't it dangerous?"
Fail. Deionized water is just normal water that has had all of the mineral ions remove (sodium, calcium, iron, etc).