I had gone to a trip to Chennai. While I was sitting in a restaurant a man excused himself and sat at my table. He began to eat idlis one after the other. As soon as one plate was finished he ordered more. I was discreetly watching him and was stunned. After he finished his last idli, he took a big gulp of water and while smiling he said, "The last one I ate was the 100th idli in five days. Each day I ate 6 more idlis than the previous day. Can you tell me how many I ate yesterday?".