Mathematics, 21.01.2020 23:31 gingerham1
The lifetime of a 2-volt non-rechargeable battery in constant use has a normal distribution with a mean of 516 hours and a standard deviation of 20 hours. the proportion of batteries with lifetimes exceeding 520 hours is approximately
a. 0.4207
b. 0.2000
c. 0.5793
Answers: 2
![P(X520)=1-P(x\leq520)\\\\=1-P(\dfrac{x-\mu}{\sigma}\leq\dfrac{520-516}{20})\\\\=1-P(z\leq0.2)\ \ [\because\ z=\dfrac{x-\mu}{\sigma}]\\\\ =1-0.5793\ \ [\text{By z-table}]\\\\=0.4207](/tpl/images/0464/7179/074ac.png)
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