Teacher and Student

Teacher : "Can anyone give me an example of Coincidence?"
Student : "Sir, my mother and father got married on the same day same time."

Teacher : How old is ur father.
Student : As old as I am.
Teacher : How is it possible?
Student:   He became father only after I was born.

Teacher : There is a frog,Ship is sinking,potatoes cost Rs 3/kg .Then,what is my age?
Student : 32 yrs.
Teacher : How do you know?
Student : Well,my sister is 16 yrs old and she is half mad.

Teacher : Paul, what is the chemical formula of Water?
Student : H,I,J,K,L,M,N,O
Teacher : What is this?
Student : Well!! you said it is H2O.