Suppose electricians come in two types: competent and incompetent. Both types of electricians can get certified, but for the incompetent types, certification takes extra time and effort. Competent ones have to spend M months preparing for the certification exam; incompetent ones takes twice as long. Certified electricians can earn 125 (thousand dollars) each year working on building sites for licensed contractors. Uncertified electricians can earn only 80 (thousand dollars) each year in freelance work; licensed contractors won't hire them. Suppose the cost of preparing for the exam is 3 (thousand dollars) per month for a competent and 5 (thousand dollars) per month for an incompetent type.

Each type of electrician's payoff is equal to their salary minus the total cost of preparing for the certification exam, i.e. (cost per month*number of months spent preparing).

What is the range of values of M for which a competent electrician will choose to use certification as a signaling device but an incompetent one will not? In other words, for what values of M would certification be a credible signal that leads to a separating equilibrium?

M should be greater than ____ and less than _______.