Question 1125226
low = [0,5)
average = [5,10)
high = [10,40)
critical = [40,+infinity)


[0,5) translates to 0 <= x < 5
[5,10) translates to 5 <= x < 10
[10,40) translates to 10 <= x < 40
[40,+infinity) translates to 40 <= x < +infinity


x represents the demand for electricity.


the assumption is that the demand can't be less than 0 and that it has no upper limit.


here's a reference on interval notation.


<a href = "http://www.coolmath.com/algebra/07-solving-inequalities/03-interval-notation-01" target = "_blank">http://www.coolmath.com/algebra/07-solving-inequalities/03-interval-notation-01</a>