for a practice question, it asked for the circumference of a circle, and the radius was 10. In case you don't know how circles work, you calculate the circumference by multiplying the radius by 2, then by pi. I did that, and I got 31.1415926526 or something like that. Since I had memorized it, I ended up typing the first 7 decimal points, since they were just like pi. However, since the digit after the 6 was 5, I got the question wrong, even though all the digits I used were correct. This is one of the dumbest problems with khan academy. I got punished for taking a risk, and I think this site sucks because of little things like this.