A variable can have lots of different values - as opposed to a constant which has only one. That is why it is called a variable!
No. A blank cell has a numerical value of zero.
Any form of numerical measurement can be a dependent variable (or an independent one).
what mathematicians agreed on an so that numercial expressions would have only one value?
the order of operations
It is a real number.
It is 1.
This will be a math function. Each choice is only going to have one answer in this kind of function.