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In a city 2500 electric lamps are installed for street lighting. The lamps come from a different manufacturer and have a mean burning life of 1040 hours. We know from past experience that the distribution of burning lives approximates a normal distribution.The 50th lamp fails after 809 hours. Approximately what is the standard deviation of burning lives for this set of lamps?

Question

smile and help me ...

In a city 2500 electric lamps are installed for street lighting. The lamps come from a different manufacturer and have a mean burning life of 1040 hours. We know from past experience that the distribution of burning lives approximates a normal distribution.The 50th lamp fails after 809 hours. Approximately what is the standard deviation of burning lives for this set of lamps?

amistre64 · Answer

what is your sample proportion?

amistre64 · Answer

this isnt a chi^2 test is it ....  im guessing its a binomial adjustment of the sample:$$s=\sqrt{pq/n}$$

anonymous · Answer

what do you mean?

anonymous · Answer

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i study this rule