lavatory tests show that the lives of light bulbs are normally distributed with a mean of 750 hours and a stoandard devotion of
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Answer:
Step-by-step explanation:
From the given information:
the mean
= 2300
Standard deviation =
Standard deviation (SD) = 214.4761
TO find:
a)
From the Z-table, since 5.595 is > 3.999
P(x > 3500) = 0.0001
b)
Here, the replacement time for the mean
= 0.25
Replacement time for the Standard deviation
For 115 component, the mean time = (115 × 20)+(114×0.25)
= 2300 + 28.5
= 2328.5
Standard deviation =
=
=
=
=
= 214.482
Now; the required probability:
From the Z-table, since 8.376 is > 3.999
P(x > 4125) = 1 - 0.9999
P(x > 4125) = 0.0001