Please ignore my handwriting and trying to answer. Trying to figure out this pro

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Please ignore my handwriting and trying to answer. Trying to figure out this problem but having some difficulty. Thanks! Question 1) (10 Points) The charge life of a certain lithium ion battery for camcorders is formally distributed with a mean of 90 minutes and standard deviation of 30 Minutes .What is the probability that a random sample of 10 batteries of this type have a mean charge life of less than 75 minutes? 2 Score Pop man 9o -75-90 Would it be unusual for a random sample of 20 batteries of this type to have a mean charge life Of less than 75 minutes ?

Explanation / Answer

Ans:

mean=90

standard deviation=30

sample size,n=10

standard error of mean=30/sqrt(10)

z=(75-90)*sqrt(10)/30=-1.58

P(z<-1.58)=0.0571

Now,when sample size,n=20

z=(75-90)*sqrt(20)/30=-2.24

P(z<-2.24)=0.0125

As,when n=20,probability of mean battery life being less than 75 <0.05,so it is unusual.

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