Think of pi as infinity. It never ends. You might mean "3.14" as an approximation of pi, though.
A expression in maths is a collection of terms without an equality sign.
Its maths
"tenth"
What symbol
division
Oh, dude, 2x in math just means you're multiplying 2 by x. It's like saying, "Hey, let's take 2 and x and make them best friends by multiplying them together." So, if x is 5, then 2x would be 2 times 5, which equals 10. Math can be cool like that, you know?
circle
direction
Related to.
Adding
The mean is usually the arithmetic mean - there are other means in maths. For a set of numbers, the arithmetic mean is the sum of the numbers divided by the number of numbers.