Fire !!! - an engineer, a physicist and a mathematician - Joke

In a hotel an engineer, a physicist and a mathematician are sleeping when a fire breaks out.

The engineer wakes up, notices the fire, grabs the next fire extinguisher and starts spraying.

 After what seems hours of heroic fighting the fire is gone and he goes to sleep again.

But the fire breaks out again. The physicist wakes up, notices the fire, grabs the fire extinguisher. Stares at the fire for some minutes, does some calculations in his head - air flow, humidity, thermodynamic whatever - and then - with one blow from the extinguisher at the right point the fire is out and he goes to sleep again.

But the fire breaks out again. 
The mathematician wakes up, notices the fire, sees the extinguisher - "aaaah, the problem is solvable"  
and goes to sleep again.

Mathematicians - This is the way they do it - Joke

A psychologist is doing a study on the different ways in which engineers, physicists, and mathematicians do things. In the first part of the study, an engineer, a physicist, and a mathematician are each taken into a different room, having a table and having a book on the floor, and asked to do a simple task: to move the book from the floor to the table.

The engineer looks at the book, picks it up, and puts it on the table. The physicist looks at the book, calls in her graduate student, and has her graduate student pick up the book and put it on the table. The mathematician looks at the book, does a few calculations, picks it up, and puts it on the table.

In the second part of the study, the three are each taken into a different room, having two tables and having a book on one of the tables, and asked to do another simple task: to move the book from one table to the other. The engineer looks at the book, picks it up, and moves it to the other table. The physicist looks at the book, calls in her graduate student, and has her graduate student pick up the book and move it to the other table. The mathematician, without hesitation, picks up the book, drops it on the floor, and says, "There! I have reduced the problem to one to which a solution is known to exist."