Many consumer alarm clocks have a snooze button that is
calibrated for 9 minutes. it sounds like an odd
decision, isn't it? Many people would think a 10-minute snooze
interval would make more sense. So were the designers asleep?
Why 9 minutes?

solve it as fast as you can.........

in a group of 200 people, everybody has a non burning candle. One person has a matchstick so that he can light his candle. With this candle he walks to somebody else and lights a new candle. Then everybody with a burning candle will look for somebody without a burning candle, and if found they will light it. This will continue until all candles are lit. Suppose that from the moment a candle is lit it takes exactly 30 seconds to find a person with a non burning candle and light that candle. From the moment the first candle is lit, how long does it take before all candles are lit?