None. They will never find a bulb that burns as brightly as the old one.
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Seven. One to install the new bulb and six to figure out what to do with the old one for the next 10,000 years.
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the barman says "Oi - get out! We don't want your type in here"
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None: they just deny that the bulb ever went out in the first place.
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One, but she'll be on the phone for five hours telling all her friends about it.
or