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Name: Norman
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Question:
If the probability of being struck by lightning is 1 in 600,000, what is the probability of being struck twice?



Replies:
Norman,

In general, the probability of some occurrence with known probability happening twice to the same individual would be a product of the independent probabilities.

In your example, this would mean 1/600,000 times 1/600,000 or 1/360,000,000,000.

Just a comment on this result...such a probability would represent the chance for a random occurrence assuming the original probability was calculated from random occurrences. This probability might be much higher for someone who tends to golf, mountain climb, fish, etc during lightning storms.

It also presumes that the individual could survive the first strike, which unfortunately might not be very likely.

Thanks for using NEWTON!

Ric Rupnik


Norman,

Lightning does not know whether you have been struck previously. After you are struck, you have a 1 in 600,000 chance of being struck a second time. The probability of being struck twice can be worked out as follows. Consider 600,000 sets of events. In the first 599,999 you are never struck. In the last you are struck at least once. This is the 1 in 600,000 chance of being struck at least once. Make each of these sets 600,000 events. All of the first 599,999 sets of 600,000 events are "never struck"(359,999,400,000 events). In the last set of 600,000 events, the first 599,999 are "only struck once". The last is "struck more then once". This is a total of 360,000,000,000 events. The probabilities are:

never struck: (599,999 in 600,000),or (359,999,400,000 in 360,000,000,000)

struck exactly once: (599,999 in 360,000,000,000),or essentially (1 in 600,000)

struck more than once: 1 in 360,000,000,000 (1 in 360 billion)

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College



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