One day in the teahouse a man asked Nasreddin, "How much older are you than your brother?"
Nasreddin sat in thoughtful silence for almost a minute before he finally answered, "I must now be three years older than he is."
"I do not understand your hesitation in answering the question," the man commented. "What took you so long?"
Nasreddin answered this question without hesitation. "I had to calculate, of course! Last year, I heard my brother tell someone that I am two years older than he is. So, since I was two years older last year, and I am one year older this year than I was last year, then I must now be three years older than he is."
Nasreddin paused to drink a sip of his tea. "At this rate," he added reflectively, "I will eventually be old enough to be his grandfather!"