Question

9.2 An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, find a 96% confidence interval for the population mean of all bulbs produced by this firm.

Answer 1

Answer:

765,795 = 96%

Step-by-step explanation:

confidence interval = 0.04  

The Za/2 theorem = 1/2 = 0.04/2 = 0.02= /x = 720z

If ; 0.02 = 2.05  then the interval is 780-2.05 x 40/√30 x 780+2.05 x 30/√30 = 765,795 = 96%

We see 40/ √30 which is found in equation of finding the sample mean at point /x = 720z

σ 40/ n√30 = 7.3029674334 and is simply a fraction of /x 720z

By normal distribution we find

The 96% confidence interval for the population mean of all bulbs = 765,795

As 765, x 1.04 = 795 = 765, 795

To find Sampling mean.

The Sampling Distribution of the Sample Mean. If repeated random samples of a given size n are taken from a population of values for a quantitative variable, where the population mean is μ (mu) and the population standard deviation is σ (sigma) then the mean of all sample means (x-bars) is population mean μ (mu).

Confidence Level z*-value

80% 1.28

90% 1.645 (by convention)

95% 1.96

96% 2.05

98% 2.33

99% 2.58