need help on B Homework: HW #8 (Ch 8) Save HW Score: 7 14%, 1.5 of 21 pts Score:

Question

need help on B

Homework: HW #8 (Ch 8) Save HW Score: 7 14%, 1.5 of 21 pts Score: 0 of 1 pt 8.1.25 The shape of the distrbution of the time required to get an oil change at a 10-minute ol-change facility is unknown. However, records indicate that the mean time is 5 of 21 (2 complete) E Question Help 11.5 minutes, and the standard deviation is 43 minutes. Complete parts (a) through (c)below (a) To compute probabilities regarding the sample mean using the normal model what size sample would be required:? Choose the required sample size below A. The nomal model canot be used if the shape of the distrbution is unknown O B. The sample size needs to be less than 30 C. The sample size needs to be greater than 30 D. Any sample size could be used (b) What is the probability that a random sample of n-40 oil changes results in a sample mean time less than 10 minutes The probability is approximately (Round to four decimal places as needed.)

Explanation / Answer

Solution:- Given that mean = 11.5 min, sd = 4.3 min

(b) For n = 40

P(X < 10) = P(x-?)/(?/sqrt(n)) < (10 - 11.5)/(4.3/sqrt(40)))
= P(Z < -2.2062)
= 0.0136

  

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