Depends, if you're looking for the raw score then you have a continuous ordinal variable. If you have range of number of car accidents, then you have an interval variable.
Number is not a variable data type.
That's a dependent variable, I believe.
Yes, IF the variable has been declared, has a value, and is of a numerical type such that your addition operator can perform the operation on the number and the value of that type variable. The compiler or interpreter will look up the variable's value, substitute it for the variable, and perform the addition just as if your statement used two numbers. First example: If your number is an integer and your variable is of type real, almost any addition operator can successfully add the two. Second example: If your number is a real and your variable is a character type (with a value, say, of "Smith"), the addition will obviously fail. In many languages, however, variables of type Boolean may be handled arithmetically, as the value True equals 1 and False is zero.
A valid variable data type is any variable of a type known to the compiler.
If an experiment compares an experimental treatment with a control treatment, then the independent variable (type of treatment) has two levels: experimental and control. If an experiment were comparing five types of diets, then the independent variable (type of diet) would have 5 levels. In general, the number of levels of an independent variable is the number of experimental conditions.
The Dependent Variable
A random variable.