A school inspector asked the class, "If length of the platform is 200 metres and speed of the train is 100 kilometres what should be my age?"
Noting the absurdity of the question, a clever student answered, "Fifty years, sir." The answer was absolutely correct.
The inspector was astounded. He asked the boy his method of calculation. "Simple, sir," the boy replied, "I have an elder brother aged 25 years and everybody calls him half mad!"