The breakdown voltage of a certain type of diode has a mean 39.8 V and standard deviation 0.72 V. If 81 diodes are randomly selected, what is the probability that the average breakdown voltage exceeds 40 V?
Solution :
Given that ,
mean = = 39.8
standard deviation = = 0.72
_{} = / n = 0.72 / 81 = 0.08
P( > 40) = 1 - P( < 40)
= 1 - P[( - _{} ) / _{} < (40- 39.8) / 0.08]
= 1 - P(z < 2.5)
= 1 - 0.9938
= 0.0062
Probability = 0.0062
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