**A mathematician found out that a pipe was leaking, so he called a plumber.**

**The plumber changed a gasket and asked for $100.**

**“But how is it possible? You’ve been working for only 10 minutes and it takes me full week to earn $100”, exclaimed the mathematician.**

**“Well, that’s why I became a plumber but let me tell you something – I’ll give you the address of my company go there and say that you want to work as a plumber and don’t mention that you are a mathematician.”**

**And so the mathematician did soon he earned quite a lot of money.**

**But the company decided to educate the plumbers and send them to primary school on the first day the mathematician was asked to write the equation for the surface of a circle on the blackboard.**

**He could not remember it, but he wanted to use integral calculus to derive it.**

**However, he made some error and obtained a negative result.**

**He repeated the calculations twice, thrice – and still obtained a negative result.**

**He looked stressed at the class and found all the fellow plumbers shouting to him, “Change the range of integration! Change the range of integration!”**