The doctor wants to question them to see if they are ready for society.

He says to one, "How much is 8 times 5?"

The first inmate says, "139."

He asks the second inmate, how much is 8 times 5?

The reply is "Wednesday."

He asks the third inmate the same question.

The inmate says, "8 times 5 is 40."

The doctor is elated!

That's great. How did you figure that out?

"Simple; I just divided 139 by Wednesday."